Wiring log cabins

Danieljk · 09-09-2020 2:24pm #1

Hi guys,

getting a lot of log cabins and sheds to be wired.

Just looking to see the different ways that other electricians have been doing this, most efficient etc.
In terms of installing sub boards and rcbo at both ends or alternative ways to this.

Cheers,
Daniel

09-09-2020 3:04pm

Danieljk wrote: »

In terms of installing sub boards and rcbo at both ends or alternative ways to this.

Hi Daniel.
What do you mean by this?

Zarco · 09-09-2020 3:47pm

2011 wrote: »

Hi Daniel.
What do you mean by this?

Whatever he means ,he's mistaken about it

Danieljk · 09-09-2020 5:28pm

2011 wrote: »

Hi Daniel.
What do you mean by this?

Hi 2011,

Im looking to see how different electricians here are wiring log cabins. It is very popular these days, to have a log cabin installed in gardens. In regards to bringing power to these log cabins I was wondering what methods are being used by electricians of experience. Are you guys extending a socket and lighting circuit off existing circuits in the house or bringing a larger SWA cable from an RCBO inside the house, into another RCBO in a sub board inside the cabin. Then having an MCB for a lighting and socket circuit.

Do you know what I mean?

Thanks

Danieljk · 09-09-2020 5:29pm

Zarco wrote: »

Whatever he means ,he's mistaken about it

Hi Zarco,

can you elaborate on what I am mistaken about? Are you a qualified electrician?

Thanks

alan4cult · 09-09-2020 5:35pm

My shed which is wired for a good few years now is 10mm SWA coming off a 40A MCB to a sub board with RCD protection for both lights and sockets.

This is in a good few years.
The earth is brought along the SWA with the SWA sheath also earthed.

I'm not sure if you need to have a second rod at the shed with a rebonding to earth but I think not. Open to correction?

09-09-2020 6:13pm

Danieljk wrote: »

Hi 2011,

Im looking to see how different electricians here are wiring log cabins. It is very popular these days, to have a log cabin installed in gardens. In regards to bringing power to these log cabins I was wondering what methods are being used by electricians of experience. Are you guys extending a socket and lighting circuit off existing circuits in the house or bringing a larger SWA cable from an RCBO inside the house, into another RCBO in a sub board inside the cabin. Then having an MCB for a lighting and socket circuit.

Do you know what I mean?

Thanks

Yes I understand. It’s a good discussion to have.

It is best not to have RCD’s in series as you can not predict with certainty which one will trip and it won’t bring anything to the party. The only exception is with TT systems.

So I would feed a sub board in the cabin from an MCB and install RCDs here for final circuits (or better still use RCBOs).

Zarco · 09-09-2020 8:53pm

Danieljk wrote: »

Hi Zarco,

can you elaborate on what I am mistaken about? Are you a qualified electrician?

Thanks

Rcbos at both ends

alan4cult · 09-09-2020 9:48pm

There's nothing wrong with an RCBO on both ends provided it protects that circuit only. If it was an RCD on both ends then yes it could trip out the entire main board sockets if it's setup that way.

Also the test switch on many RCDs will cross live to neutral so a downstream test will also knock out the upstream RCBO.

Well I don't see an issue with it but an MCB from main board is the usual.

Zarco · 09-09-2020 10:10pm

alan4cult wrote: »

There's nothing wrong with an RCBO on both ends provided it protects that circuit only. If it was an RCD on both ends then yes it could trip out the entire main board sockets if it's setup that way.

Also the test switch on many RCDs will cross live to neutral so a downstream test will also knock out the upstream RCBO.

Well I don't see an issue with it but an MCB from main board is the usual.

It's either not recommended or not allowed without a time delay

Can't remember which

10-09-2020 9:31am

alan4cult wrote: »

There's nothing wrong with an RCBO on both ends provided it protects that circuit only. If it was an RCD on both ends then yes it could trip out the entire main board sockets if it's setup that way.

Ask yourself this:
What are the advantages of having RCD protection at both ends of a cable?

Zarco · 10-09-2020 9:35am

The rules have a section on the issue although they don't seem to ban it outright

Zarco · 10-09-2020 9:42am

536.3.1

This rule can be interpreted as meaning that you shouldn't RCD protect the distribution circuit to the cabin unless there's discrimination

10-09-2020 9:44am

Zarco wrote: »

The rules have a section on the issue although they don't seem to ban it outright

Just because something is not banned does not mean that it is a good design.

In some limited cases RCD’s in series make sense such as a TT installation.
But in that case the devices have very different differential trip values.

Tuco88 · 10-09-2020 10:22am

Is there not a rule about external cables from a domestic dwelling being rcd protected? I know lighting is.

Getting messy putting an S type rcd at the main db etc...

10-09-2020 10:28am

Tuco88 wrote: »

Is there not a rule about external cables from a domestic dwelling being rcd protected? I know lighting is.

Getting messy putting an S type rcd at the main db etc...

I am not aware of any such rule. I only work in the industrial sector but I can’t see why such a rule for domestic installations would exist (it certainly does not exist for industrial installations). I wouldn’t like to supply a sub distribution board from an RCD. The cable for the sub distribution board can be protected in other far more practical ways that avoid the risk of nuisance tripping, expense of an RCD and issues that may be associated with it. If you were going to go down this road then you have to ask why not install RCD protection on the tails to the main board.

Zarco · 10-09-2020 10:28am

Tuco88 wrote: »

Is there not a rule about external cables from a domestic dwelling being rcd protected? I know lighting is.

Getting messy putting an S type rcd at the main db etc...

Doubt it very much, would be a load of nonsense if there was

stiofan85 · 10-09-2020 10:29am

I had a cabin wired up with rcd at both ends by a reci. Then went to sell the house and needed a PIR for thre whole house and another reci said no to the double rcd, put it onto an mcb without rcd in the main board and then just the sub board with rcd in the cabin.

Power was via dedicated 6mm swa in a conduit 3ft below the lawn. I think I had lights, and two socket circuits - one was dedicated to washing machine and dryer, with an isolator, both circuits on rcd. No rcd on lights I think. There was also a master switch in the sub board for the whole cabin.

I was surprised in the difference in approaches as I thought it would all be standardised.

10-09-2020 10:35am

stiofan85 wrote: »

I had a cabin wired up with rcd at both ends by a reci.

I’m not saying it is not allowed, I’m saying it is daft.

Then went to sell the house and needed a PIR for thre whole house and another reci said no to the double rcd, put it onto an mcb without rcd in the main board and then just the sub board with rcd in the cabin.

A much better job in my opinion.

Power was via dedicated 6mm swa in a conduit 3ft below the lawn. I think I had lights, and two socket circuits - one was dedicated to washing machine and dryer, with an isolator, both circuits on rcd. No rcd on lights I think. There was also a master switch in the sub board for the whole cabin.

Sounds good to me.

I was surprised in the difference in approaches as I thought it would all be standardised.

I’m not

stiofan85 · 10-09-2020 10:36am

2011 wrote: »

I’m not saying it is not allowed, I’m saying it is daft.

A much better job in my opinion.

Sounds good to me.

I’m not

Hope the detail helps the op

Zarco · 10-09-2020 10:41am

stiofan85 wrote: »

I had a cabin wired up with rcd at both ends by a reci. Then went to sell the house and needed a PIR for thre whole house and another reci said no to the double rcd, put it onto an mcb without rcd in the main board and then just the sub board with rcd in the cabin.

Power was via dedicated 6mm swa in a conduit 3ft below the lawn. I think I had lights, and two socket circuits - one was dedicated to washing machine and dryer, with an isolator, both circuits on rcd. No rcd on lights I think. There was also a master switch in the sub board for the whole cabin.

I was surprised in the difference in approaches as I thought it would all be standardised.

It is standardized

RCDs have uses but protecting buried SWAs isn't one of them

10-09-2020 11:28am

stiofan85 wrote: »

Hope the detail helps the op

If you read the questions asked in the OP I think that you will see that it does

helimachoptor · 10-09-2020 11:31am

stiofan85 wrote: »

I had a cabin wired up with rcd at both ends by a reci. Then went to sell the house and needed a PIR for thre whole house and another reci said no to the double rcd, put it onto an mcb without rcd in the main board and then just the sub board with rcd in the cabin.

Power was via dedicated 6mm swa in a conduit 3ft below the lawn. I think I had lights, and two socket circuits - one was dedicated to washing machine and dryer, with an isolator, both circuits on rcd. No rcd on lights I think. There was also a master switch in the sub board for the whole cabin.

I was surprised in the difference in approaches as I thought it would all be standardised.

This is what my elctrcian did, he's a friend, but ours for 10, run of about 75M from the board.

We took the offer of having the cabin wired up by the cabins electrical company, sparks dropped cables for 8 downlights, 4 double sockets and 2 external lights and wanted to run it off a plug in the kitchen :eek:

10-09-2020 11:44am

helimachoptor wrote: »

This is what my elctrcian did, he's a friend, but ours for 10, run of about 75M from the board.

What did your electrician friend do? You have quoted a post that describes 2 wiring methods. One which as an RCD at each end and one that doesn’t.

We took the offer of having the cabin wired up by the cabins electrical company, sparks dropped cables for 8 downlights, 4 double sockets and 2 external lights and wanted to run it off a plug in the kitchen :eek:

Why did you take this offer ??

helimachoptor · 10-09-2020 12:12pm

2011 wrote: »

What did your electrician friend do? You have quoted a post that describes 2 wiring methods. One which as an RCD at each end and one that doesn’t.

Why did you take this offer ??

Sorry thought I edited the post I quoted.
swa goes from the main board to rcbo.

My friend wasn't around and it needed to be done while the cabin was being assembled

Danieljk · 10-09-2020 12:22pm

2011 wrote: »

Just because something is not banned does not mean that it is a good design.

In some limited cases RCD’s in series make sense such as a TT installation.
But in that case the devices have very different differential trip values.

This is a very valid point.

These days it is common to put outdoor lighting, bathroom lighting and outdoor sockets on an RCBO.

So is it right, wrong or indifferent to come from a 32a MCB on the RCD side to a sub board with an RCBO in the shed then feeding a normal 20a and 6a MCB for sockets and lighting. Or an RCBO from the board to a sub board in the cabin feeding a 32a MCB or RCBO again?

Zarco · 10-09-2020 1:16pm

Danieljk wrote: »

This is a very valid point.

These days it is common to put outdoor lighting, bathroom lighting and outdoor sockets on an RCBO.

So is it right, wrong or indifferent to come from a 32a MCB on the RCD side to a sub board with an RCBO in the shed then feeding a normal 20a and 6a MCB for sockets and lighting. Or an RCBO from the board to a sub board in the cabin feeding a 32a MCB or RCBO again?

They're both wrong

No selectivity and you're creating a nuisance with the lighting in the shed going off due to the sockets

Danieljk · 10-09-2020 1:34pm

Zarco wrote: »

They're both wrong

No selectivity and you're creating a nuisance with the lighting in the shed going off due to the sockets

Good point, thanks for that input! Whats your opinion on 32a MCB (non RCD side) from the board run with a 6mm SWA to an enclosure with 10a RCBO (lights) and 20a RCBO (sockets)?

10-09-2020 4:14pm

2011 wrote: »

I’m not saying it is not allowed, I’m saying it is daft.

Not if you cascade the trip thresholds.

10-09-2020 4:34pm

Sir Liamalot wrote: »

Not if you cascade the trip thresholds.

As I already stated (post #14).

It is still not something I would avoid.

Tuco88 · 10-09-2020 5:39pm

2011 wrote: »

I am not aware of any such rule. I only work in the industrial sector but I can’t see why such a rule for domestic installations would exist (it certainly does not exist for industrial installations). I wouldn’t like to supply a sub distribution board from an RCD. The cable for the sub distribution board can be protected in other far more practical ways that avoid the risk of nuisance tripping, expense of an RCD and issues that may be associated with it. If you were going to go down this road then you have to ask why not install RCD protection on the tails to the main board.

I'm only in the pharmaceutical side. When they make changes to domestic rules or RECI make suggestions if your not in that industry its hard to keep up.

Wiring log cabins

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