Low Voltage Distribution at Home

Chet T16

Hi all,

Two questions.

Are there any regulations or anything i need to be aware of for running my own low voltage supply to each room in the house? I am thinking in the region of 12-24v but would want to push this as high as i can while keeping within the bounds of what i'm allowed to do.

As i understand it anything that is to be wired into the mains needs to be done by a certified electrician i.e. anything thats not plugged in to a socket. Is this correct or a generalisation i've picked up somewhere?

Thanks

SpaceTime

Just be careful, some people make the mistake of thinking low voltage = no risk.

There's no risk of electric shock, but there's a significant fire hazard with low voltage systems that are carrying large amounts of power.

I've seen low voltage halogen light wiring literally melt where inadequate wiring was used.

You'll also have issues with voltage drop over long runs of wire and you'll need to use heavier gauge wires.

What are you connecting to this proposed system and could you step the 230V down locally instead?

2011

Chet T16 wrote: »

Are there any regulations or anything i need to be aware of for running my own low voltage supply to each room in the house? I am thinking in the region of 12-24v but would want to push this as high as i can while keeping within the bounds of what i'm allowed to do.

What do you mean by "keeping within the bounds of what i'm allowed to do"?

As far as I know there is nothing in the Restricted Works Decision Paper about 12 or 24V supplies somehow being exempt (if that is what you mean).

The work will still have to comply with ET101, be carried out by a registered electrical contractor and be certified.

As i understand it anything that is to be wired into the mains needs to be done by a certified electrician i.e. anything thats not plugged in to a socket. Is this correct or a generalisation i've picked up somewhere?

Have a read of the Restricted Works Decision Paper (link above), that should clear it up for you.

Leaving the Restricted Works aside, this is really not a good idea.
As SpaceTime has stated above there are risks and disadvantages associated with a 12 or 24V distribution system. This is why it never "caught on".

Chet T16

In each room there'll be a remote radiator valve which operates on 24v ac/dc and has a startup current of 250mA and operational on 125mA. There will also be a sensor node which i hope will be in the region of 100mA @ 5v.

Ideally i'd like to use CAT5 cable to power both over 4 of the wires (the other 4 will be used for serial comms) which is why i wanted to run as high a voltage as i could.

I wanted to avoid the mains if it meant i needed someone else to do it for me to keep it legit.

Chet T16

2011 wrote: »

What do you mean by "keeping within the bounds of what i'm allowed to do"?

As far as I know there is nothing in the Restricted Works Decision Paper about 12 or 24V supplies somehow being exempt (if that is what you mean).

The work will still have to comply with ET101, be carried out by a registered electrical contractor and be certified.




Have a read of the Restricted Works Decision Paper (link above), that should clear it up for you.

Leaving the Restricted Works aside, this is really not a good idea.
As SpaceTime has stated above there are risks and disadvantages associated with a 12 or 24V distribution system. This is why it never "caught on".

What i meant was if the regulations somewhere said that anything below X volts fails out of the bounds of requiring the work to be completed by a registered electrician then this is what i'd work with.

By setting up my own system to run parallel to the mains i would be free to do as i wish with it. Once i had an electrician install my 12/24/48v transformer that is.

2011

Chet T16 wrote: »

What i meant was if the regulations somewhere said that anything below X volts fails out of the bounds of requiring the work to be completed by a registered electrician then this is what i'd work with.

The regulations do not cover this, the Restricted Works paper above does.
If there is an exemption you will find it there.
I would expect that your 24V system will need a mains voltage connection somewhere though (as you appear to have acknowledged).

gctest50

Battery powered and wireless any use ? bit safer than running LV everywhere

http://zwave-products.co.uk/shop/article_206/danfoss

Battery lifetime 2 years

wexie

Would you not just save yourself the headache and get some POE adapters / injectors?

http://www.ebay.co.uk/itm/48V-24V-AC-Adapter-Supply-For-PASSIVE-PoE-Box-Power-Over-Ethernet-Injector-Kit-/121221202679?pt=LH_DefaultDomain_0&var=&hash=item1c3958c2f7

or even a POE switch : http://www.ebay.co.uk/itm/NETGEAR-8-port-10-100Mbps-ProSafe-Switch-with-POE-FS108P-/301112143706?pt=UK_Computing_NetworkSwitches_RL&hash=item461baeaf5a

2011

Hi OP, I have had a good think about this.
I take it all back

Apart from the 230VAC supply I imagine that you would be permitted to run and terminate the cabling you describe. Why? Because alarm installers, satellite installers and network point installers do not have to be registered electrical contractors.

ted1

you can put a three pin plug on it!

jeepers101

2011 wrote: »

Apart from the 230VAC supply

Would that not fall under minor works?

Chet T16

gctest50 wrote: »

Battery powered and wireless any use ? bit safer than running LV everywhere

I'm not completely against wireless but when wired is available i'll go with it. I'll be building this system myself (i'm an electronic engineer) and want complete control over everything. Anyway i'll need to power the sensor nodes too.

wexie wrote: »

Would you not just save yourself the headache and get some POE adapters / injectors?

http://www.ebay.co.uk/itm/48V-24V-AC-Adapter-Supply-For-PASSIVE-PoE-Box-Power-Over-Ethernet-Injector-Kit-/121221202679?pt=LH_DefaultDomain_0&var=&hash=item1c3958c2f7

or even a POE switch : http://www.ebay.co.uk/itm/NETGEAR-8-port-10-100Mbps-ProSafe-Switch-with-POE-FS108P-/301112143706?pt=UK_Computing_NetworkSwitches_RL&hash=item461baeaf5a

I'm not using ethernet, i'll be using rs485 serial. As far as i recall PoE works by biasing the data lines and even if i could make it work it doesn't seem to actually solve any issue

2011 wrote: »

Hi OP, I have had a good think about this.
I take it all back

Apart from the 230VAC supply I imagine that you would be permitted to run and terminate the cabling you describe. Why? Because alarm installers, satellite installers and network point installers do not have to be registered electrical contractors.

Well this is good news then! Alarms are mostly (all?) 24v aren't they?

jeepers101 wrote: »

Would that not fall under minor works?

I had to google that term, it seems the comment i made about "anything not plugged into a socket" is wrong. It looks like adding a transformer or SMPS into an existing circuit would be allowed. I wouldn't mind if i needed to get this done anyway - once i have freedom to work on the LV side

2011

Chet T16 wrote: »

Well this is good news then!

Hopefully!
I am just giving an opinion.

Alarms are mostly (all?) 24v aren't they?

Generally alarms are 12VDC

I had to google that term, it seems the comment i made about "anything not plugged into a socket" is wrong. It looks like adding a transformer or SMPS into an existing circuit would be allowed. I wouldn't mind if i needed to get this done anyway - once i have freedom to work on the LV side

"Minor works" do not have to be carried by a registered electrical contractor and are defined in the Restricted Works link above.

Chet T16

2011 wrote: »

Hopefully!
I am just giving an opinion.



Generally alarms are 12VDC



"Minor works" do not have to be carried by a registered electrical contractor and are defined in the Restricted Works link above.

Yeah but your opinion suits me so i'll take it as fact

It gives a couple of examples of 'minor works' which are far beyond what i would need to do. Although it might give me more scope for converting the 230v supply locally and direct to whatever voltage i need rather than sending this intermediate source from a central location

liveandnetural

this sprung to mind
https://www.youtube.com/watch?v=XDf2nhfxVzg&list=TLyeX7cBjM2kJ3uK3XxgIgR4ieozshck0Y

Chet T16

liveandnetural wrote: »

this sprung to mind
https://www.youtube.com/watch?v=XDf2nhfxVzg&list=TLyeX7cBjM2kJ3uK3XxgIgR4ieozshck0Y

I've rewound a microwave transformer so it outputs 1.5v at silly amps, thats fun to play with.

cast_iron

2011 wrote: »

Apart from the 230VAC supply I imagine that you would be permitted to run and terminate the cabling you describe. Why? Because alarm installers, satellite installers and network point installers do not have to be registered electrical contractors.

Out of curiosity, is there a cut-off voltage written in stone anywhere?

I would have guessed 50V and above, as over this figure is deemed to be quite harmful for humans to touch.

frankmul

Restricted works decision paper keeps referring to LV systems which are 50 to 1000 v ac, I guess anything below 50 vac is not restricted work.

2011

frankmul wrote: »

Restricted works decision paper keeps referring to LV systems which are 50 to 1000 v ac, I guess anything below 50 vac is not restricted work.

That makes sense alright.

<50V is "ELV" (Extra Low Voltage)

Bruthal

cast_iron wrote: »

I would have guessed 50V and above, as over this figure is deemed to be quite harmful for humans to touch.

It would want to be a decent few volts above 50 to do much harm. Even 110v is very mild on dry hands.

markad1

What about belden 8777 cable?

http://www.belden.com/techdatas/english/8777.pdf

cast_iron

Bruthal wrote: »

It would want to be a decent few volts above 50 to do much harm. Even 110v is very mild on dry hands.

A centre tapped 110V yes, but RMS 110V? If I've termed that right.

Bruthal

cast_iron wrote: »

A centre tapped 110V yes, but RMS 110V? If I've termed that right.

No, the 110v direct. 55v barely perceivable on hands, if at all. 110v is perceivable, but very mild.

Again, most assume 110v = decent shock. It wont, unless there is a very good contact area, wet hands, etc, and even then it wont approach anything like what 230v will inflict in the same circumstances.

2011

markad1 wrote: »

What about belden 8777 cable?

http://www.belden.com/techdatas/english/8777.pdf

What about it?

cast_iron

Bruthal wrote: »

No, the 110v direct. 55v barely perceivable on hands, if at all. 110v is perceivable, but very mild.

Again, most assume 110v = decent shock. It wont, unless there is a very good contact area, wet hands, etc, and even then it wont approach anything like what 230v will inflict in the same circumstances.

Is there not an argument in there about the length of time in contact though?

Say a 110V supply came in contact to the skin and (as you say) the person barely perceived it (if they were drunk or something ) and it remained in contact. I think a low current flowing, caused by 110V contact, over time will eventually lead to serious harm to tissue and the nervous system.

It's a rather theoretical argument, but I think it's the logic behind the 50V number.

Bruthal

cast_iron wrote: »

Is there not an argument in there about the length of time in contact though?

Say a 110V supply came in contact to the skin and (as you say) the person barely perceived it (if they were drunk or something ) and it remained in contact. I think a low current flowing, caused by 110V contact, over time will eventually lead to serious harm to tissue and the nervous system.

It's a rather theoretical argument, but I think it's the logic behind the 50V number.

Not all theoretical. Got 110v before, ammeter, you can work out the rest yourself. Couldnt get it to read above 10ma even with wet hands as far as I remember. All in the name of science:)

It was perceivable, but very mild.

The 50v number is just a voltage they deem safe. There are other hazards to a given voltage besides direct shock hazard, but its likely it is purely on that basis that it is the level picked. Id guess the people who decide these things would have the same assumptions as most when it comes to electrical shocks at given voltages.

cast_iron

Bruthal wrote: »

Not all theoretical. Got 110v before, ammeter, you can work out the rest yourself. Couldnt get it to read above 10ma even with wet hands as far as I remember. All in the name of science:)

It was perceivable, but very mild.

To you yes, with your big, leathery, old man hands
I would imagine a small child would probably perceive more than that. And a shock directly across the chest. And domestic pets, etc would have different body resistances.

There's a table I remember being taught that gave the current readings a body could take and the damage inflicted over different time scales of exposure to the current flowing. I forget the figure now though.

Bruthal

cast_iron wrote: »

To you yes, with your big, leathery, old man hands

No leathery hands here. Small hands that look like they never did any work. There was added water as well.

I would imagine a small child would probably perceive more than that. And a shock directly across the chest.

A 12v battery terminal in each hand would have current flowing across the chest too. A child might be more at risk from a given current level, but unlikely to receive any more of a dangerous shock from 110 volts than anyone else.

And domestic pets, etc would have different body resistances.

Hard for them to have a 110v line in each hand though:pac:

There's a table I remember being taught that gave the current readings a body could take and the damage inflicted over different time scales of exposure to the current flowing. I forget the figure now though.

Water is a toxin at a certain amount taken, actually acts as a toxin. Takes a fair bit of effort to bring it to effect though.

And alcohol, over 2 units a day and damage is done. Thats the way it goes though.

frankmul

cast_iron wrote: »

To you yes, with your big, leathery, old man hands
I would imagine a small child would probably perceive more than that. And a shock directly across the chest. And domestic pets, etc would have different body resistances.

There's a table I remember being taught that gave the current readings a body could take and the damage inflicted over different time scales of exposure to the current flowing. I forget the figure now though.

Some thing along these lines, https://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html

markad1

Chet T16 wrote: »

In each room there'll be a remote radiator valve which operates on 24v ac/dc and has a startup current of 250mA and operational on 125mA. There will also be a sensor node which i hope will be in the region of 100mA @ 5v.

Ideally i'd like to use CAT5 cable to power both over 4 of the wires (the other 4 will be used for serial comms) which is why i wanted to run as high a voltage as i could.

I wanted to avoid the mains if it meant i needed someone else to do it for me to keep it legit.

2011 wrote: »

What about it?

In answer to the cable he could use.

Bruthal

markad1 wrote: »

In answer to the cable he could use.

Perhaps a quote of the poster in the reply to help them see.

markad1

Bruthal wrote: »

Perhaps a quote of the poster in the reply to help them see.

ok

Bruthal

frankmul wrote: »

Some thing along these lines, https://www.osha.gov/SLTC/etools/construction/electrical_incidents/eleccurrent.html

They seem a bit overly simplistic in calculations in that. One thing is right though, the skin resistance is quickly reduced as voltage increases. Far more severe shocks are inflicted with 230v than 110, and again when it steps to 400v.

It would be some shock to receive 2 amps though, even from 1000 volts, which id say would be unlikely. That would be heading for destruction of body parts. Got a nice one from 2.5kv before. Horrendous whack. Tried a moving solenoid 1000v esb test lamps on it after it happened. Instantly ended its useful life.

frankmul

Bruthal wrote: »

They seem a bit overly simplistic in calculations in that. One thing is right though, the skin resistance is quickly reduced as voltage increases. Far more severe shocks are inflicted with 230v than 110, and again when it steps to 400v.

It would be some shock to receive 2 amps though, even from 1000 volts, which id say would be unlikely. That would be heading for destruction of body parts. Got a nice one from 2.5kv before. Horrendous whack. Tried a moving solenoid 1000v esb test lamps on it after it happened. Instantly ended its useful life.

Where did you get 2.5 kv from. Discharge lighting?

Bruthal

frankmul wrote: »

Where did you get 2.5 kv from. Discharge lighting?

It was a commercial microwave oven transformer. Two magnetrons in microwave. It was only giving half power so the procedure was to disconnect one and heat some water to find which was the faulty one by elimination.

Managed to hit hand off the spade connection and other hand was on the steel frame of the microwave wall bracket. Such a whack like nothing ever before or since.

frankmul

Bruthal wrote: »

It was a commercial microwave oven transformer. Two magnetrons in microwave. It was only giving half power so the procedure was to disconnect one and heat some water to find which was the faulty one by elimination.

Managed to hit hand off the spade connection and other hand was on the steel frame of the microwave wall bracket. Such a whack like nothing ever before or since.

Ouch!

Bruthal

frankmul wrote: »

Ouch!

It was horrendous, only in contact for fraction of second, after which hands went involuntarily down to sides, with fingers clenched. Was like that for a good few seconds. 20 years ago now.

Chet T16

Bruthal wrote: »

It was a commercial microwave oven transformer. Two magnetrons in microwave. It was only giving half power so the procedure was to disconnect one and heat some water to find which was the faulty one by elimination.

Managed to hit hand off the spade connection and other hand was on the steel frame of the microwave wall bracket. Such a whack like nothing ever before or since.

One hand in the pocket!

I've been looking at this problem for a while. I'd run an entire house on DC if I could.
Given a house with a DC supply. Last time I dropped the issue I speculated that after the first two rooms the expense involved in low loss cabling compared to the elevated efficiency losses of inverters/transformers outweighs the overall transportability of AC.
Seems to me to run AC from a DC source back to a device local DC supply is the most cost effective.
You may find otherwise given that you are only pulling down mA.

Bruthal

Chet T16 wrote: »

One hand in the pocket!

Time machine?

Chet T16

Bruthal wrote: »

Time machine?

Future reference although i suspect you knew it already and definitely stick to it now

Chet T16

Sir Liamalot wrote: »

I've been looking at this problem for a while. I'd run an entire house on DC if I could.
Given a house with a DC supply. Last time I dropped the issue I speculated that after the first two rooms the expense involved in low loss cabling compared to the elevated efficiency losses of inverters/transformers outweighs the overall transportability of AC.
Seems to me to run AC from a DC source back to a device local DC supply is the most cost effective.
You may find otherwise given that you are only pulling down mA.

From reading about cat5 it looks like 24v DC at 1A is well within spec using a single wire, i'll be using two.

My sensor boards will use minimal power, the radiator valves would be my only concern but even then i don't see an issue.

Bruthal

Chet T16 wrote: »

Future reference although i suspect you knew it already and definitely stick to it now

Well there was no need for a hand in pocket while working on them microwaves. Cable with spade connector safely tied up, and no hands near the microwave except to press the start button on the front panel.

My problem was I left the spade end hanging out, and brushed off it when I went to scratch the head or something.

After that it was cover the cable end and tie it up properly.

Stranded cable is more appropriate for DC.

Bruthal

Sir Liamalot wrote: »

Stranded cable is more appropriate for DC.

Any reasons you're thinking of?

Its more flexible, better to terminate, better against vibration, but they can apply in ac or dc, although heavy DC currents are prevalent for engine starting etc where vibration resistance is needed.

Current capacity in dc would depend more purely on CSA than in ac probably, apart from needing good terminations.

tomdempsey200

better connections with stranded or flexible I suppose

Bruthal

tomdempsey200 wrote: »

better connections with stranded or flexible I suppose

Yes but that would apply to both AC and DC

CSA is significant. DC only travels the surface of the conductor unlike AC which vibrates along the whole core. Always fighting voltage drop on elaborate DC systems.
I'm changing tack and currently looking at DC for batteries and AC coupling for loads on demand as a more more feasible way to reduce system losses.

Cat V comes in solid and stranded core...only learned recently, I always ended up with solid core before on jobs. Can't abide the stuff myself, it's good stuff for an install as data cable with Cat V compatible equipment (pointless as as DMX to Cat V, power etc...). It's kinda throw away cable though if you're doing turnovers...too flimsy. I'd often use 7 core automotive trailer cable with preference if I need that many lines.

brightspark

Sir Liamalot wrote: »

CSA is significant. DC only travels the surface of the conductor unlike AC which vibrates along the whole core.

Any source for that?

My understanding was that Eddy currents caused the skin effect in AC systems, the effect increasing with the frequency.

2011

Sir Liamalot wrote: »

CSA is significant.

With AC and DC, yes.

DC only travels the surface of the conductor unlike AC which vibrates along the whole core.

I assume that you are talking about the Skin Effect?

It is actually the other way around.
With AC the electric current flows mainly at the outer edges of the conductor (or skin).
The skin effect causes the effective resistance of the conductor to increase.
This effect increases as the frequency increases.
This reduces the effective cross sectional area of the conductor.

I think that you are over thinking this.
To reduce volt drop use a cable with a larger cross sectional area.

2011

2011 wrote: »

I think that you are over thinking this.

haha..yeah usually! Not likely to stop soon either...don't worry I do understand the inherent values in KISS, I said looking. It'll be years before I make my mind up.
The price of copper is the limiting factor in conductor size for me in terms of home distribution.

Thanks for the correction, I was convinced contrary, it corresponded neatly as my wiring applications are a combination of high flexibility, vibration requirements; automotive, small scale campervan off grid electrics, solar PV, wind turbines and rolling in and out of gigs...seeing these (mostly) DC sources were always on stranded cables it reinforced my misinterpretation . I read of the skin effect, can't remember where and guess I confused the context.