110v rcbo

M cebee

anyone know if the standard rcbo's etc. do 110v

it's 55-0-55 and i'll be using C16's

i'm told they do .doesn't seem to be much info available

DublinDilbert

Well it is a current based device, so the only thing that will matter if its capable of breaking the circuit at a particular voltage. As your within the voltage ratting you should be grand, just look at it like a fuse.

I presume your using a center tapped trafo to generate the 110V, so i would guess you'd need a 2 pole MCB.

M cebee

2 pole rcbos

it exceeds 50v to earth so afaik you gotta fit rcd protection

DublinDilbert

M cebee wrote: »

2 pole rcbos

it exceeds 50v to earth so afaik you gotta fit rcd protection

I might be completely wrong, but would a standard rcbo not do?

2011

In theory a 230V RCBO would work (as you say it is a current based device), but in practice this would not be done.

M cebee

so they're available in 110v?
any link for a mainstream brand?

Bruthal

DublinDilbert wrote: »

I might be completely wrong, but would a standard rcbo not do?

Standard RCBO definitely will work, they will work with any voltage as long as its AC, and obviously within reason. The test button is the only thing that might not work at lower voltages as less current is drawn through the one winding to cause it to trip when pressing the test button. Test button might work at 110v though.

One other thing is if the 110v is from an isolated secondary side of transformer it wont work either, but once the centre tap is earthed it will.I thought i seen isolated ones used before in certain setups, where the secondary side is not earthed at all. In this scenario an RCD or RCBO wont trip on earth fault, as there is no earth fault path. Although maybe the old age is catching up and it was all a dream.

M cebee

you wouldn't need earth-fault protection if secondary was isolated:D

The wholesalers weren't familiar with 110v rcbos anyhow

Bruthal

M cebee wrote: »

you wouldn't need rcd protection if secondary was isolated:D

i haven't really looked into it much yet.The wholesalers weren't familiar with 110v rcbos anyhow

True but it was somethin that was asked for before on job i was involved in which had isolated secondary, and i said exactly that, whats the point of having it. But its worth mentioning anyway. Because the test button will still work making some believe its working away on an isolated setup that does`t actually need it. Really you would wonder is it needed on 55v centre tapped setup either. As 55 volts is barely if at all perceivable to touch. But i suppose it makes the installation more sensitive to earth faults.

M cebee

50v to earth is the upper-limit for no earth-fault protection afaik

in the UK you wouldn't need rcd for 110v sockets unless they were outside afaik

Bruthal

M cebee wrote: »

50v to earth is the upper-limit for no earth-fault protection afaik

in the UK you wouldn't need rcd for 110v sockets unless they were outside afaik

Yes i think it is 50 volts, but someone would want to have taken an overdose of iron to recieve a shock from 50 volts. On temporary traffos on sites they were just double pole mcb`s were they. Cant even remember now its that long since been on a site. Almost retired now with this recession.

Bruthal

The only thing in an RCD that makes it 230 volt is the test button circuit. Also the current interupting capacity is given for 230 volts. Other than that they will work on 10 volts ac or 110 or 220 all the same once either leg is earthed or in the case of 110 volts the centre tap is earthed. Even if you get an RCD and get a 1.5 volt battery and get wire from each end onto one pole of the RCD that will trip it, the initial increase in current from zero to whatever the battery can deliver in short circuit will momentarilly induce current into the trip coil. Another piece of useless info.

M cebee

afaik they(gennys)don't require rcd for power tools .

the risk is lower as there is no exposed metalwork( as in an installation

with 110v workshop sockets) with the potential for more dangerous fault currents

i think i'm right there?

rcd's are used with genny's sometime's to ensure quicker fault disconnection

a fault at the end of a long lead may take a while to trip the genny

i've forgotten a lot of the details

Bruthal

M cebee wrote: »

afaik they(gennys)don't require rcd for power tools .

the risk is lower as there is no exposed metalwork( as in an installation

with 110v workshop sockets) with the potential for more dangerous fault currents

i think i'm right there?

rcd's are used with genny's sometime's to ensure quicker fault disconnection

a fault at the end of a long lead may take a while to trip the genny

i've forgotten a lot of the details

Well its more to do with the risk of people receiving electric shock that RCD is used more so than the size of fault current that could develop. 250 volts will in theory at least give someone 25 times the shock that 50 volts will. In reality its probably more as the higher voltage tends to break down the initial resistance of skin more than lower voltage, particularly dry skin.
In dry conditions a person can come into contact with live 230 volt mains and feel nothing once not in contact with any other neutral/earth. Im sure a few here will say no that cant happen, but it is a fact. So in reality touching one pole of 110v will result in no shock at all, even if the person is in contact with an earth also. Even if it is felt, it will be barely perceivable.

Im not sure myself of all the requirements much the same as yourself.

M cebee

1.automatic disconnection(if mcb doesn't ensure it)

2.electric shock

3. 'fire hazard' caused by fault currents

that's about it for rcds afaik

Bruthal

Also as matter of interest the 3 phases between secondary side of 38kv ESB transformers and the primary side of the 10KV transformers are isolated systems, but you still be fried if touch one phase, even though they are Delta/Delta with no star point.

Bruthal

M cebee wrote: »

1.automatic disconnection(if mcb doesn't ensure it)

2.electric shock

3. 'fire hazard' caused by fault currents

that's about it for rcds afaik

1. Cookers, lights, etc dont have RCD to backup MCB, and in fact the real backup is in having fuses in the circuit to protect against large fault currents. A short between the 2 poles in 110v wont operate the rcd and will be a higher fault current than earth fault current. (which might backup the reason for having RCD in the 110v due to lower earth fault current)
As i was saying yesterday the sockets on sites did`t have RCD`s on the 110v temporary supplies.

2. Well 55 volts wont give much of a shock, even 110v is unlikely to be severe, and a shock involving 110 wont trip RCD unless there is a contact with earth also, and at 55 volts to earth a person would be unlikely to reach the RCD trip current anyway.

3. Fires are generally caused by bad connections in electrical, or faulty appliances. High fault currents usually mean a good fault path, and also mean fast operation of protective devices.

Certainly not a bad thing having an RCD on 110v socket circuits. I dont really think its of big benefit though.
Just more thoughts on it.

M cebee

bad connections. but also leakage current can cause fires

the rcds for fire can be rated at 300mA

Bruthal

M cebee wrote: »

bad connections. but also leakage current can cause fires

the rcds for fire can be rated at 300mA

A well we could go on all night and day about them. They definitely would assist in fire protection alright.

RoundyMooney

robbie7730 wrote: »

Also as matter of interest the 3 phases between secondary side of 38kv ESB transformers and the primary side of the 10KV transformers are isolated systems, but you still be fried if touch one phase, even though they are Delta/Delta with no star point.

That's due to capacitance. 20kV feeders are an earthed system (well, kind of), however. The transformers do have star points btw.

An RCD on an isolated system is just a placebo.

Bruthal

RoundyMooney wrote: »

That's due to capacitance. 20kV feeders are an earthed system (well, kind of), however.

An RCD on an isolated system is just a placebo.

Capacitance is right, and the the RCD on isolated system a placebo is right also. As i said, i seen them goin in somewhere before and asked whats the point of that, but i never found out as ended up on different job. It was some medical lab so maybe they liked placebo`s

Bruthal

RoundyMooney wrote: »

That's due to capacitance. 20kV feeders are an earthed system (well, kind of), however. The transformers do have star points btw.

An RCD on an isolated system is just a placebo.

Well i must be gettin old, i thought i remember the 38 secondary being delta and 10kv primary being delta also (from workin on them), that does`t mean they were though as my memory seems brutal these days, maybe the 38kv secondary was star to monitor earth faults to bring up the 38kv station earth fault alarm. Them 10kv lines dont trip on earth faults, or is that different now as well. Luckily im now a carpenter
Obviously urban city centre areas with underground cables have higher capacitive effect on MV to HV cables

RoundyMooney

10kV primaries are delta.

EF tripping is used mainly in urban settings, where there's a greater proportion of cable, or on 20kV. The star point there is brought out through a 4ohm resistance to reduce stresses on the system under EF conditions.

Cable vs overhead capacitance ratio is taken as 20:1.

10kV earth faults on overhead used to bring up an alarm through a voltage sensing relay on the star point, but nearly all feeders will now use faulty phase earthing to export the fault back to the station and maintain supply while reducing fault current at the site.

38kV feeders use arc suppression, to neutralise as much as possible the capacitive effect, again from the star point. Impedance relays are used for line protection here.

HTH.

Bruthal

RoundyMooney wrote: »

10kV primaries are delta.

EF tripping is used mainly in urban settings, where there's a greater proportion of cable, or on 20kV. The star point there is brought out through a 4ohm resistance to reduce stresses on the system under EF conditions.

Cable vs overhead capacitance ratio is taken as 20:1.

10kV earth faults on overhead used to bring up an alarm through a voltage sensing relay on the star point, but nearly all feeders will now use faulty phase earthing to export the fault back to the station and maintain supply while reducing fault current at the site.

38kV feeders use arc suppression, to neutralise as much as possible the capacitive effect, again from the star point. Impedance relays are used for line protection here.

HTH.

Amazing the stuff ye forget with time. Although the faulty phase earthing was`t around when i was as far as i remember, sounds like a great idea.

RoundyMooney

It came out in the late eighties/very early nineties.

That and an ASC setup are being trialled on 20kV atm.

Bruthal

RoundyMooney wrote: »

It came out in the late eighties/very early nineties.

That and an ASC setup are being trialled on 20kV atm.

Yes probably, thats when i was finishing apprenticeship, i think the 20kv setup was just starting then as well. Or preperations for it.

RoundyMooney

It was indeed. I was kitting out mobile interfaces around '94 or '95.

The plan was to roll it out nationally, and convert 38s to 110.

It may happen yet!