Power to shed

gooddarts10

Hi I’m wondering what is the best way to get a 16 amp socket for a welder fitted in a shed around 30 meters from the distribution board. What size cable etc.
Any advice welcome thank you

Hmob

What type welder is it?

Is there anything else apart from the welder?

Hmob

Don't know a whole lot about welders,my experience with the older type welders was simply oversizing the supply cable and sticking in a D type mcb

The little bit of research I did there on the inverter type tells me the inrush isn't an issue but they may need the newer type F RCD

Open to correction on that

gooddarts10

Hmob wrote: »

What type welder is it?

Is there anything else apart from the welder?

Mig with a 16amp blue plug and no that’s the only thing

Hmob

Well if you're only wiring the welder

I'd prob be looking at a C type mcb for the 16amp socket at the main board and then a rcd at the welder end

Don't like to be giving out specifics if it's a diy install?

punisher5112

Swa cabl buried or cable in suitable red ESB conduit at 600 mm depth run from board to shed.

10 sq but I'd say 16sq will be the one to use as you will most likely use lighting and other things along with the welder.

Hmob

punisher5112 wrote: »

Swa cabl buried or cable in suitable red ESB conduit at 600 mm depth run from board to shed.

10 sq but I'd say 16sq will be the one to use as you will most likely use lighting and other things along with the welder.

Was going to say

He'll need electric lighting at a minimum

No doubt 13amp sockets as well for grinders and the like

gooddarts10

Hmob wrote: »

Well if you're only wiring the welder

I'd prob be looking at a C type mcb for the 16amp socket at the main board and then a rcd at the welder end

Don't like to be giving out specifics if it's a diy install?

Definitely won’t be a DIY job I’m just trying to gauge costs of materials etc

Hmob

gooddarts10 wrote: »

Definitely won’t be a DIY job I’m just trying to gauge costs of materials etc

As punisher said you'll need more than the welder

10sq swa

Sub-board and wiring in shed

Cost :get a few quotes

gooddarts10

Hmob wrote: »

As punisher said you'll need more than the welder

10sq swa

Sub-board and wiring in shed

Cost :get a few quotes

Would you recommend 10sq and not 16sq

Hmob

gooddarts10 wrote: »

Would you recommend 10sq and not 16sq

Your REC will need to calculate onsite and decide

...Ghost...

Would he even need 10?

Maybe my sums are off, but based on a 20 amp load and 35m run I am getting 2.5mm^2. I would bump that to 4mm^2.

Academically speaking, why is 10 or 16 being recommended?

disclaimer: not an electrician.

alan4cult

Yeah I figured 6mm cable too for the extra few bits that would be needed. 10mm probably for piece of mind as better to go to a board and then take a 6.

Hmob

alan4cult wrote: »

Yeah I figured 6mm cable too for the extra few bits that would be needed. 10mm probably for piece of mind as better to go to a board and then take a 6.

I didn't calculate anything.

I just picked 10 but figured 6 would do

16 is definitely overkill unless there's unknowns

punisher5112

Welder will draw a huge current, lighting not so much and sockets for other bits such as a heater and so on.

Really all depends on what realistically is going to be used.

I myself for that would go with the at a minimum 6 but prefer 10.

Hmob

There's no regulation that says you can't just oversize and leave spare capacity.

May not be relevant here

Cost is c.100 extra for 10

Hmob

punisher5112 wrote: »

Welder will draw a huge current, lighting not so much and sockets for other bits such as a heater and so on.

Really all depends on what realistically is going to be used.

I myself for that would go with the at a minimum 6 but prefer 10.

Do these inverter welders draw these huge currents?

Not sure if that's what he's using ?

Hmob

...Ghost... wrote: »

Would he even need 10?

Maybe my sums are off, but based on a 20 amp load and 35m run I am getting 2.5mm^2. I would bump that to 4mm^2.

Academically speaking, why is 10 or 16 being recommended?

disclaimer: not an electrician.

Forget the 2 and the 4, whatever your sums say.

Start at 6 even if calculations say lower

2011

Hmob wrote: »

16 is definitely overkill unless there's unknowns

There are definitely unknowns, for a start we don't know the total cable run, we need to know this to calculate the volt drop. This is made up of:
1) The tails from the ESB meter to the main DB, length = ? - I have seen 4 mm sq. used here :eek:
2) The cable from the main DB to the shed DB, length = 30m
3) The cable from the shed DB to the welder socket, length, = ?

We also need to know:
1) What the design current for each of the above sections of cable.
2) Rating and type of protective devices.

...Ghost...

We can only go off what the OP is saying. If he is getting an REC, there's nothing to worry about. No harm building in a bit extra, but going 6 times higher than needed (16sq) would be wasteful and needlessly expensive.


The OP says 30m. Building in some buffer, I calculated 35m underground cable. He says 16Amps needed, I added a buffer to get to 20 for lights and a cd player or a whatever. The voltage drop is about 12 at that distance and 2.5sq meets the criteria. 4sq well covers it.


However, if the OP adds wants to add a heater, a 2.5kW will draw around 10Amps, so if that is a possibility, then 4sq will cover him. I would however recommend 6sq. Going for 10sq would not be unreasonable, but it also would not be necessary unless the OP wants to go full on man cave.

punisher5112 wrote: »

Welder will draw a huge current, lighting not so much and sockets for other bits such as a heater and so on.

Really all depends on what realistically is going to be used.

I myself for that would go with the at a minimum 6 but prefer 10.

2011 wrote: »

There are definitely unknowns, for a start we don't know the total cable run, we need to know this to calculate the volt drop. This is made up of:
1) The tails from the ESB meter to the main DB, length = ? - I have seen 4 mm sq. used here :eek:
2) The cable from the main DB to the shed DB, length = 30m
3) The cable from the shed DB to the welder socket, length, = ?

We also need to know:
1) What the design current for each of the above sections of cable.
2) Rating and type of protective devices.

Hmob wrote: »

Forget the 2 and the 4, whatever your sums say.

Start at 6 even if calculations say lower

punisher5112

I got a bit ahead of myself when I seen welder, here was me going back to my maintenance days and 3phase ones.

Putting in 4sq and then thinking after oh yeah a heater, kettle, bar full on man cave bar ;-).....

I'd definitely be going 6sq at a minimum.

Unless the op really has no need for these extras.

180A TIG & Stick inverter welder.

I can run that off my 4kVA battery inverter generator.
No cables, no dino juice.

2011

...Ghost... wrote: »

The OP says 30m. Building in some buffer, I calculated 35m underground cable. He says 16Amps needed, I added a buffer to get to 20 for lights and a cd player or a whatever. The voltage drop is about 12 at that distance and 2.5sq meets the criteria. 4sq well covers it.

But you only did a partial volt drop calculation (only on the cable between the main DB and the shed I assume) and you have no idea what the earth fault loop impedance would be so with that cable you have no idea whether the protective device will trip within the required time.

...Ghost...

2011 wrote: »

But you only did a partial volt drop calculation (only on the cable between the main DB and the shed I assume) and you have no idea what the earth fault loop impedance would be so with that cable you have no idea whether the protective device will trip within the required time.

For that reason, I say bump up to the next level. But i'm not an electrician, so I always ask for verification at the end. I've just recently had to size cables for a project and I take the same approach. In my case, I increased the size by 50%. Same process when I was running cable to a filter house/shed. Years later, constantly running, no problems so far thankfully. The electrician I use to complete the installation has never questioned the cable size and knew what loads would be drawn.

2011

...Ghost... wrote: »

For that reason, I say bump up to the next level.

You can’t simply assume that any preexisting volt drop or earth fault loop impedance issue at the main distribution board will be resolved by this approach.
Is there a preexisting issue? Maybe, we can't possibly know.

It is possible that a 16 mm sq. may be the smallest acceptable cable size to comply with the rules if the existing main DB is “on the edge” of what is permitted. Again we don't know.

But i'm not an electrician, so I always ask for verification at the end.

It is good that you get it verified.

It may have been better to state this in post number 20. In this post despite the lack of sufficient information to make such a claim you say that a 16 mm sq. cable would be six times larger than required :eek:

I've just recently had to size cables for a project and I take the same approach.

From what we have seen approach does not account for the volt drop on the final circuit within the shed and the volt drop on the tails to the main DB so perhaps a recalculation would be best.

Years later, constantly running, no problems so far thankfully.

I’m delighted that you got away with it. I’ve seen installations without any earths and fuses replaced with nails. No issues ever but I still wouldn’t recommend that approach. It would be irresponsible to take this approach to wiring on the basis of that someone else has been lucky enough not to have not to have an incident.

However it’s is possible that your setup has not had to operate under fault conditions. Under these circumstances it may not perform as well as one would hope. For example if the earth fault loop impedance is too high the protective device may not operate quickly enough or it may not operate at all.

The electrician I use to complete the installation has never questioned the cable size and knew what loads would be drawn.

.....and maybe your cables are sufficiently sized, I certainly hope they are.
I must warn you that method you have applied for cable sizing does not comply with the rules require and does not align with best practice.

I don’t mean to give you a hard time but you need to understand that mains voltage is potentially lethal and that a proper assessment needs to be carefully carried out before making conclusive statements with regard to cable size.

2011

2011 wrote: »

I’ve seen installations without any earths and fuses replaced with nails.

Amateurs! At least use an M6 brass thread!

punisher5112

Sir Liamalot wrote: »

Amateurs! At least use an M6 brass thread!

Or feck it just bypass the fuse altogether, sure they cost money they did....

...Ghost...

2011 wrote: »

You can’t simply assume that any preexisting volt drop or earth fault loop impedance issue at the main distribution board will be resolved by this approach.
Is there a preexisting issue? Maybe, we can't possibly know.

It is possible that a 16 mm sq. may be the smallest acceptable cable size to comply with the rules if the existing main DB is “on the edge” of what is permitted. Again we don't know.



It is good that you get it verified.

It may have been better to state this in post number 20. In this post despite the lack of sufficient information to make such a claim you say that a 16 mm sq. cable would be six times larger than required :eek:



From what we have seen approach does not account for the volt drop on the final circuit within the shed and the volt drop on the tails to the main DB so perhaps a recalculation would be best.



I’m delighted that you got away with it. I’ve seen installations without any earths and fuses replaced with nails. No issues ever but I still wouldn’t recommend that approach. It would be irresponsible to take this approach to wiring on the basis of that someone else has been lucky enough not to have not to have an incident.

However it’s is possible that your setup has not had to operate under fault conditions. Under these circumstances it may not perform as well as one would hope. For example if the earth fault loop impedance is too high the protective device may not operate quickly enough or it may not operate at all.



.....and maybe your cables are sufficiently sized, I certainly hope they are.
I must warn you that method you have applied for cable sizing does not comply with the rules require and does not align with best practice.

I don’t mean to give you a hard time but you need to understand that mains voltage is potentially lethal and that a proper assessment needs to be carefully carried out before making conclusive statements with regard to cable size.

I did say in post 12 I am not electrician. I questioned the recommendation of 16sq from an academic point of view. I also said as the OP will be getting a REC to do the job, there should be no problem. Had the OP intended to do the work himself, I'd have advised against it and would have advised any cable sizes were verified by the REC in any case.


When calculating anything electrical, I always where possible err very much on the side of caution. But that doesn't mean it's ok to just accept very much larger (and more expensive) cables for a job that wouldn't need it. If the home owner has a better idea, he could at least question why the electrician is opting for 120sq instead of 6 or 10. It wouldn't be a stretch to say that an electrician might use larger cable just because he doesn't have enough of the smaller gauge.


You are correct to say that we don't know the circumstances. I only base my sums off what was provided and gave some room for error. We are talking about electricity, so it's ok to give someone a hard time if they are talking nonsense, so long as the reasons are highlighted. We are good


Without testing the real world situation of the OP, we can only speculate to calculate. The voltage drop of 12 was a high estimate for the distance. Theoretical calculations are based on ideal conditions. This is why I bump up the the size. I should have considered a few branches from the circuit in the shed. Bumping the length to 50m to carry a max load of 20Amps using 6sq cable and assuming a rare copper resistivity of 0.0171 Ohms @25 degrees Celsius, we get: Voltage Drop = 50 x 20 x 0.0171/6
Voltage Drop = 2.85
Reduce to 4sq and we get 4.28V drop.
Even at 30Amps using 4sq, the V drop is 6.4 (theoretically).



Of course, an electrician will have to check everything out and the OP should unquestionably seek the advice and services of same.

2011

...Ghost... wrote: »

When calculating anything electrical, I always where possible err very much on the side of caution.

Erring on the side of caution means looking at the big picture ie. a holistic approach is needed. Your focus has been limited to one of (at least) three cables that would determine how fit for purpose the new wiring would be.

In this case just for the volt drop we have a minimum of 3 cables to consider:
1) The existing cable from the meter to main DB.
2) The new cable from main DB to the shed.
3) The cable from the shed sub-DB to the furthest point.

The total volt drop will be the sum of the above 3.

Points to consider include:
1) Current carrying capacity.
2) Earth fault loop impedance. The existing cable from the meter to the main DB will be a factor in this.
3) Future capacity, there can be plenty of debate about this. Some are reluctant to pay additional for this.
4) The nature of the load.

I did say in post 12 I am not electrician.

That is a fair point.

But that doesn't mean it's ok to just accept very much larger (and more expensive) cables for a job that wouldn't need it.

This is very true. Whatever cable size is selected should be based on a proper assessment.