Two Tt Supplies Taken To A Single Board

[Manator]

I do not ask many questions but I thought I would throw this in for discussion.

I have a job to do where the building was split into two many years ago, as such the original supply was split externally to provide two separate meters.Now the building is to be converted into one again.

I plan to leave the meters in situ but move one of the supplies and take both supplies into a three phase board so it only requires one main switch. the circuits can then be split to provide clinical area metering and general use plus lighting metering.

(both supplies are from the same phase)

I am upgrading the earthing at the moment there is only one rather ancient rod in place and Ra readings are very poor.

The supply is giving me 60amps per supply.

Do you have any observations on my intentions, or can you think of a better way to do it?

 

[ProDave]

Only that the DNO should be moving the supplies and moving the meters?

Presumably the two supplies and meters are separate from each other now, and one needs relocating to get the two meters in the same place.

Why a 3 phase board?  Why not two single phase boards with a REC4 isolator in front of them?

 

[NozSpark]

Is this 3ph board metal clad??

Other than that, so long as it displays a dual supply sticker (which goes without saying) then I can't see a problem.

 

[Manator]

Hi PD, the supply and meter are staying where they are, I am just coming off the meter to get the power into one place. I am thinking of the costs which is why I want one board rather than two, but have yet to cost up the alternatives.

 

[ProDave]

Two single phase boards and a REC4 will be cheaper than one 3 phase board?

Unless you know a source of cheap 3 phase boards.

A 3 phase would probably confuse the hell out of some future sparky who wonders why the new circuit he connected to L3 does not work. (but arguably he should not touch it if he can't work that out)

 

[steptoe]

Two single phase boards and a REC4 will be cheaper than one 3 phase board?

Unless you know a source of cheap 3 phase boards.

A 3 phase would probably confuse the hell out of some future sparky who wonders why the new circuit he connected to L3 does not work. (but arguably he should not touch it if he can't work that out)

msl:

you used cheap & 3phase in the same sentence 

 

[batty]

Would it be possible to change earthing is this a medical install? Metalclad board would probably require front end RCD being TT is this the job you were looking at using Daves RCBO's?

 

[kerching]

I know of some very cheap 3 phase boards......made by an anagram cgd.........absolutely freaking carp

You can have good

You can have cheap

You can have quick

Unfortunately you only get to choose 2 of the above......

Merely thought it worth mentioning

 

[batty]

I won't be buying three phase stuff through wholesalers again they certainly mark them up buying online is much better.

 

[apprentice87]

I would MUCH prefer the two single phase boards and the REC4 [better still, two REC2's]... Be a whole lot easier to fathom out for the next bloke that comes along, and, also, i too would have thought it cheaper.

How was the supply split in the first place?? Cannot that just be "undone" and it all put back how it was once, if you see what i mean??

john...

 

[steptoe]

I would MUCH prefer the two single phase boards and the REC4 [better still, two REC2's]... Be a whole lot easier to fathom out for the next bloke that comes along, and, also, i too would have thought it cheaper.

How was the supply split in the first place?? Cannot that just be "undone" and it all put back how it was once, if you see what i mean??

john...

John, if its one installation there needs to be one point of isolation, so it needs to be a REC4

 

[Manator]

Hi John, the split was done on the outside of the building by the DNO. I cannot touch anything before the meter. The thought of using a single board was to have a single point of isolation, but I can see the argument for installing a REC4. I was going to install a 100mA s type main switch so I get discrimination, I am just playing around with all the options. Your ideas are very welcome and are giving me more options.

 

[Sidewinder]

You're basically having a summation supply, but, in TT?

 

[SLIPSHOD & SLAPDASH]

I had a job recently just like you propose, looked like a old 3 phase head & only 2 s phase meters fitted with a link between 2 terminals in the 3 phase board. Confused me as it transpired it was single phase. We are currently trying to get the supply upgraded, its like banging your head against a wall dealing with the Dno's

 

[apprentice87]

Hi Steps,

You are right of course, never thought of that... Just thought have a separate isolator for each board. Thinking of it though, why bother with the REC's at all?? You could just turn the installation off with the incomer in the board, and if you want to isolate the submain you could do that at its origin..

john..

 

[MeFil]

Q. Do you need 120A supply ? (2 × 60A supply)

Could one supply be isolated and the other upgraded to 100A? Would that be sufficient for the demand?

 

[NozSpark]

Just thinking on this...

Could it be adventageous to keep the clinical ccts seperate to the domestic ccts?

 

[Manator]

You're basically having a summation supply, but, in TT?

Yes thats the basic idea

I had a job recently just like you propose, looked like a old 3 phase head & only 2 s phase meters fitted with a link between 2 terminals in the 3 phase board. Confused me as it transpired it was single phase. We are currently trying to get the supply upgraded, its like banging your head against a wall dealing with the Dno's

The DNO have quoted around £10,000 for the upgrade as its a rural area and a pain to get a TN supply into.

Q. Do you need 120A supply ? (2 × 60A supply)

Could one supply be isolated and the other upgraded to 100A? Would that be sufficient for the demand?

Its a big building and my initial design included 30% for future expansion, 120A will do the job though.

Just thinking on this...

Could it be adventageous to keep the clinical ccts seperate to the domestic ccts?

That is what I am intending to do, all the clinical areas will be metered from one, and all other circuits on the other.

Thanks everyone for the input, I have decided to go with two boards after pricing up all the options. I really should get my office to contact SBS dave!!

 

[sparkytim]

I have used a 20 Mod Crabtree CU and fitted 2 Main switches with a split load Busbar to accomplish a Duel Tarriff set up and just last week to split an Off peak Load over 2 Phases, labelled up clearly warning of 2 supplies etc.

 

[Manator]

Thanks sparky, interesting option.