Consumer unit query.

[ajlelectronics]

I took the lid off my 3 phase consumer unit and was a bit stunned by what I found...

The three phase is all reasonable, but the single phase circuits are all over the place. In one set of half a dozen power sockets, they appear to be connected across the three phases, which is not very sensible. The lighting circuit is also fed from one of the phases via a 6 mcb. There is no RCD protection either, despite a three phase, 13A and 16A socket installed externally so I want to sort it all out.

The CU is a MEM unit which modules are less common for, so my idea is as follows...

Leave all the three phase as is (not sure about RCD for the external 3p socket?) and take a feed from either a 40A or even the 63A mcb which is in there, to a new 18th CU with one or two RCDs and then feed all the single phase stuff exclusively from there. I have seen this one (only one at a realistic price!) and would appreciate comments. I would be happy with a 17th plastic CU but of course nobody is selling them, even though I did the installation years ago of course.

Feed from the 63A or the 40A mcb? Short length, perhaps 1m, so 6mm cable?

https://www.screwfix.com/p/refurb-british-general-fortress-16-module-10-way-populated-high-integrity-dual-rcd-consumer-unit/688ra#product_additional_details_container

 

[sparkysy]

Go on then, let's have a look at it!
I'd say if it's that bad rip it out and tidy it up properly, Fusebox TP boards are as excellent as their single phase ones, and they are cheap!

 

[ajlelectronics]

Go on then, let's have a look at it!
I'd say if it's that bad rip it out and tidy it up properly, Fusebox TP boards are as excellent as their single phase ones, and they are cheap!

I was going to photograph it earlier but my battery was flat. I will add photos when I go in to the workshop next.

 

[Robotstar5]

I try to keep sockets in the same area on the same phase like when I was adding some sockets for @Cato the existing sockets were on 1L2 so I put the additional sockets on 2L2

 

[ajlelectronics]

I try to keep sockets in the same area on the same phase like when I was adding some sockets for @Cato the existing sockets were on 1L2 so I put the additional sockets on 2L2

View attachment 466464

I thought that sockets on different phases, in the same area were verboten under the regs, due to the chances of getting the full PD connected across you between them?

 

[Robotstar5]

I thought that sockets on different phases, in the same area were verboten under the regs, due to the chances of getting the full PD connected across you between them?

I don't think it's in the current regs, but may have been in the older ones, 15th or 16th editions.

 

[MetalMonkey]

It isn't prohibited in the current regulations (not since the 14th). See here for more details:

https://electrical.theiet.org/wiring-matters/years/2018/70-may-2018/myth-busters/

There are good reasons why you may want multiple phases serving different equipment in for example a data centre.
For sockets, I would still tend to group an area on the same phase for logic if nothing else, unless there was a compelling reason to do otherwise such as load balancing. I'd still label it as well.

 

[ajlelectronics]

It isn't prohibited in the current regulations (not since the 14th). See here for more details:

https://electrical.theiet.org/wiring-matters/years/2018/70-may-2018/myth-busters/

There are good reasons why you may want multiple phases serving different equipment in for example a data centre.
For sockets, I would still tend to group an area on the same phase for logic if nothing else, unless there was a compelling reason to do otherwise such as load balancing. I'd still label it as well.

Well that's me told then! Thanks for the clarification.

What do I do about 3P protection for the outside sockets?

 

[sako243]

I thought that sockets on different phases, in the same area were verboten under the regs, due to the chances of getting the full PD connected across you between them?

Others have clarified the regulation situation but I think if it's not displayed then it should be.

I was doing some PLC testing at my old job and one test I setup which I wasn't expecting to have an issue with just didn't work. Did some investigation and discovered that in the same lab we had two benches next to each other were fed by different phases. Basically the sockets on the exterior wall were one phase and the interior wall were a different.

On my way to make a cuppa my boss at the time was chatting to the engineering director of the whole company. He called me over and asked me to update the director on the project. I said well found something a bit odd just now and explained. The directors face dropped and he asked me to measure the difference across the sockets. My boss said, we can't ask him to do that. I said I didn't mind in the slightest. Director threw his coffee in the sink and said fine, I'll do it so we don't have to ask anyone... So we both went down to the lab in question, may or may not have shoved a screw driver into the earth to stick the multimeter probes in. Yup 415V between the sockets. Director said I think that's illegal, ****... Went out of the lab and phoned facilities to get an electrician down. They phoned up and managed (at great cost) to get a contractor in an hour later and they did a quick survey and concluded it was all a mess.

A hour later an email went out saying the entire site (housed about 2000 workers) was to be shut down that weekend so that they could fully investigate the wiring. Was rather entertaining three months into my job that I caused a site wide shutdown. Luckily a lot of the servers and stuff were located elsewhere and had redundancy so didn't affect people outside of the electronics group too much.

What came back was that it was okay but every single socket and switch then got labelled with which phase and distribution board it was on and in the labs were we had sockets on multiple phases they were clearly labelled with big warning stickers. They also reshuffle a lot of the benches around so that it wasn't quite so easy to plug in test equipment into multiple benches which was the main concern.

Entertaining to be there in the least.

 

[Robotstar5]

I've seen a few commercial/industrial lighting switch banks clearly marked when they have more than one phase inside.

 

[MetalMonkey]

Circuit and DB labelling of sockets has always been the defacto standard in the commercial/industrial/military places I've worked. More documentation = more better in my book, providing it is kept accurate of course.
I would personally stick a label on anything where there is the potential for over 240V anyway, rightly or wrongly even if it is not to earth as per 514.10.1. I can't see it would make it less safe, and the regulations are only the minimum standard as they always say.

As for the lighting, I think that is more likely covered by 514.11.1, i.e. the need to have a warning if there is more than one point of isolation.
Technically of course that could apply to a lot of domestic hallway lights, but I can't imagine any warning signs would stay put very long.

As for the sockets, yes RCD protection. Especially for outdoors. Irrespective of the regs or the age of the installation, it just makes plain sense.

 

[ajlelectronics]

This is the label from the current installation, from my files. I gather that it is pre-historic and modules are scarce. It would of course be better if I could retrofit a 3 phase breaker. Would I be correct in my assumption that anything wired downwind of that RCD in single phase would be protected, or would it require a single phase RCD for those circuits?

Pictures from the installation tomorrow, so perhaps I should just say,"here it is, what do I do now to achieve the relevant protection with what I have?".

 

[Onoff]

It would of course be better if I could retrofit a 3 phase breaker.

Try these people:

Reconditioned Circuit Breakers

New & Reconditioned circuit breakers, MCB's, MCCB's, RCBO's, ACB's and Incomers.Reconditioned Circuit Breakers - if you have a requirement for any sort of post production MCB to match your existing installation, contact one of our technical team on 01

www.reconelectrical.co.uk

 

[jimbo84]

This is the label from the current installation, from my files. I gather that it is pre-historic and modules are scarce. It would of course be better if I could retrofit a 3 phase breaker. Would I be correct in my assumption that anything wired downwind of that RCD in single phase would be protected, or would it require a single phase RCD for those circuits?

Pictures from the installation tomorrow, so perhaps I should just say,"here it is, what do I do now to achieve the relevant protection with what I have?".

View attachment 466533

MEM serial numbers run backwards so that one is 24/01/1994, if you wanted a rough date of install.

The serial numbers are also a good indicator for asbestos, any MEM product after 1985 didn't contain asbestos.

 

[brightspark]

I don't think it's in the current regs, but may have been in the older ones, 15th or 16th editions.

as long as theres about ten foot gap between them its ok. any closer and plugged in appliances could be touched by someone in between any closer they need to be on the same phase

 

[MetalMonkey]

as long as theres about ten foot gap between them its ok. any closer and plugged in appliances could be touched by someone in between any closer they need to be on the same phase

Have a look at the link I posted Brightspark, that is no longer the case (not since the late 70s anyway).
The touch distance rule no longer applies.

 

[brightspark]

Have a look at the link I posted Brightspark, that is no longer the case (not since the late 70s anyway).
The touch distance rule no longer applies.

 

[brightspark]

that is true the case i was on about was in a school classroom none domestic . walls had been taken out between rooms and sockets on either side on seperate phases and ten of them ended up being 24 inch apart the kids plugging kettles in and various appliances and at the time no rcd protection

 

[sparkysy]

What do I do about 3P protection for the outside sockets?

If you put a new DB in there are 3phase 30ma RCBO's available for such cases.
How is the circuit wired?
If it's in trunking, conduit or SWA then you could fit a socket with built in 4pole RCD to protect whatever is plugged in and the user!
Toolstation do a very reasonably priced one and good quality!

Industrial RCD Socket IP67

www.toolstation.com

As for that existing DB, I still possibly have a selection of MCB's for it, no RCBO's though as I've used all of those up over the years.
I will know for sure when you post a pic of it!

If so then they used to do a clip on RCD for some of their range called an MR30, which are available still but quite eye watering prices!

https://www.cef.co.uk/catalogue/products/5077588-memshield-2-field-fit-rccb-pod-30ma-type-a-230v-ac?gad_source=1&gclid=CjwKCAjw6c63BhAiEiwAF0EH1NaOuilSanw1jAaOcdZ0tY2pxU_kSksFrxSmS7PqtdpJEKzp2IErcRoCVLEQAvD_BwE&gclsrc=aw.ds

 

[brightspark]

cheaper just to fit an external rcd in an enclosure outside the board inline / cost peanuts