Running 3 phase and single phase links from a single RCD

[fuzzytrifle]

I've got two 3 phase distribution boards in our home workshops. Both boards are protected by 4 pole RCD incomers and independently connected to a busbar chamber. Both are fitted with a combination of 3 phase and single phase MCBs.

I've just discovered that I shouldn't be running both 3 phase and single phase links from a single RCD.

There's enough room to move all of the 3 phase MCBs to one board, protected by a single RCD, and the single phase MCBs to the smaller board.

Should I convert the smaller board to a single 240V supply (I already have the conversion kit) connected to either L1 or L2, and fit it with single phase RCBOs? Or leave the board connected as it is, with the 4 pole RCD in place and spread the single phase MCBs evenly across L1, L2 and L3?

I'll be using an electrician, but wanted some opinions first before having to pay for 14 RCBOs. For all I know, it's perfectly acceptable to run both single phase and 3 phase links from an RCD incomer and the article I've just read online is incorrect. Any advice would be appreciated.

 

[flameport]

I've just discovered that I shouldn't be running both 3 phase and single phase links from a single RCD.
...
the article I've just read online

Where is this article ? - please post a link to it.

 

[ericmark]

Where did you discovered? As far as I am aware there is not rule as to separate RCD's.

Using RCBO with a three phase supply often means taking up 6 rather than 3 slots. Although I have used them they came as two separate items which I had to combine.

The problem as far as I see it most RCD testers will only work on one phase at a time so instead of the normal 6 tests you would need 18 tests on each RCD. However since tested as single phase clearly they will work with single phases.

The only problem is the built in mechanical test button normally only selects one of the three phases to test the device so testing with a proper RCD tester is more important.

In general the incomer is protected by a 300ma RCD (sometimes 100ma) where for sockets and cable protection the requirement is 30ma. As a result it is common to fit a consumer unit fed from the distribution unit to reduce the current the trip will operate at. In practice however often if something does cause the device to trip it will take out both.

 

[Spark123]

The reason of not being allowed to mix 3phase and 1phase is absolute rubbish.
There may be other reasons that mixing your loadings isn't a good idea from a single point of failure point of view but not because of the above.

 

[fuzzytrifle]

I've just discovered that I shouldn't be running both 3 phase and single phase links from a single RCD.
...
the article I've just read online

Where is this article ? - please post a link to it.

http://www.ecollege.ie/site/liu/electrical_notes/LL227.pdf

Can't remember why I was reading these notes, but found this quoted on page 11:

"It is possible to supply the single-phase loads through a three-phase RCD. This would simplify the arrangement a good deal, however it is not recommended to supply a mixture of single and three-phase loads through one RCD"

 

[JohnW2]

http://www.ecollege.ie/site/liu/electrical_notes/LL227.pdf
Can't remember why I was reading these notes, but found this quoted on page 11: ....

Maybe I need a trip to Specsavers, because I don't find it (on p11 or anywhere else) - are you sure you posted the correct link?

Kind Regards, John

 

[fuzzytrifle]

Where did you discovered? As far as I am aware there is not rule as to separate RCD's.

http://www.ecollege.ie/site/liu/electrical_notes/LL227.pdf

Quote found on page 11, under 'Neutral Connections'

I'm hoping that I can just leave the installation as it is - we've had no problems with it for the past five years and I like the idea that I can isolate each workshop independently.

 

[fuzzytrifle]

Maybe I need a trip to Specsavers, because I don't find it (on p11 or anywhere else) - are you sure you posted the correct link?

Kind Regards, John

http://www.ecollege.ie/site/liu/electrical_notes/LL227.pdf

Just tested the link and it opens as a PDF.

Regards, Steve

 

[fuzzytrifle]

There may be other reasons that mixing your loadings isn't a good idea from a single point of failure point of view but not because of the above.

So should I separate the single and 3 phase connections?

The boards are only supplying a couple of small workshops, one for my wife's kilns and the other for my woodworking machinery - just the two of us and we haven't had any problems with the installation in the last five years.

 

[JohnW2]

[http://www.ecollege.ie/site/liu/electrical_notes/LL227.pdf
Quote found on page 11, under 'Neutral Connections'

Are we looking at the same Page 11 of the same document? ...

Untitled

• JohnW2
• 23 Oct 2012
• 1

Kind Regards, John

 

[JohnW2]

So should I separate the single and 3 phase connections? The boards are only supplying a couple of small workshops, one for my wife's kilns and the other for my woodworking machinery - just the two of us and we haven't had any problems with the installation in the last five years.

FWIW, I don't see any real point in/need for you to change anything.

Kind Regards, John

 

[flameport]

This is the actual document with the correct page 11:
http://www.ecollege.ie/site/liu/electrical_notes/LL232.pdf
which has this:

It is possible to supply the single-phase loads through a three-phase RCD. This would simplify
the arrangement a good deal, however it is not recommended to supply a mixture of single and
three-phase loads through one RCD. The reasons for this are beyond the scope of Phase 2 of the
apprenticeship.

and no explanation as to why.

 

[JohnW2]

This is the actual document with the correct page 11: http://www.ecollege.ie/site/liu/electrical_notes/LL232.pdf
which has this:

It is possible to supply the single-phase loads through a three-phase RCD. This would simplify the arrangement a good deal, however it is not recommended to supply a mixture of single and
three-phase loads through one RCD. The reasons for this are beyond the scope of Phase 2 of the apprenticeship.

and no explanation as to why.

Thanks (it helps to have the correct link ). It would seem that the reasons are not only "beyond the scope of Phase 2 of the apprenticeship" but also beyond the understanding of most of us here! As has been said, in some situations there may be an argument for separation of circuits, but AFAIAA that's got nothing to do with whether they are 1-phase or 3-phase circuits.

Kind Regards, John

 

[333rocky333]

A fair bit of 3 phase equipment incorperates single phase loads anyway
3 phase ovens tend to have single phase elements and many appliances have single phase control circuits

 

[Spark123]

It would appear that the linked to document is talking about a particular installation i.e. a test bay in a College or similar over in Ireland. It could quite easily be just an opinion of a college lecturer.

It may be that their ETCI regs don't recommend that setup but there is nothing in our British Regs along those lines - my knowledge of the ETCI regs is about zero btw!