piggybacking consumer units

[PeteC]

advice needed#

I work for a solar PV company, and they're trying to streamline (for cost planning) our connection to the consumer unit. We need an extra mcb to connect onto, and most of the time customers consumer units don't have a spare way, and if they do then continual load deratings of mcbs may come into play (such as with Proteus mcbs).

It's been suggested piggy backing off the mainswitch of the con'unit with meter tails to supply a small mcb enclosure? I'm not sure if this meet regs.
The unit housing would have to be BSEN 60439-3~ mini consumer unit to supply rating
Meter tails used would have to be supply rating

But (regarding the connection point onto the main switch) ~ is this failing correct use of equipment?

Seems a henley block connection to the metertails would be a correct approach, but that involves planning service-head de and re-energising.

???

 

[JulianC]

First thing that springs to mind is the fact that it'd be bloody tricky, if not impossible to securely fit 2 x 25mm tails in a main switch terminal. I keep a spare, small CU and a Henley block in the van for those PV jobs where there isn't a spare way in the CU.

planning service-head de and re-energising.
???

Pulling the fuse takes very little in the way of planning ;-)

 

[Sintra]

Personally i think the henly block method would be the best solution. The next best IMO would be to fit a new 4 way con unit and move a circuit from original con unit into new one. This then leaves a spare way in the original con unit that can be used to feed the new con unit.

 

[PeteC]

Moving an mcb (normally garage / or end one) and new 2nd board is what I've been doing. But you then need to certify the moved circuit (specifically found that out from my 2910-10 assessor) as you,ve "altered" the circuit. If circuit is ok then the little extra R1+R2 is no prob. but if not you need to put right before you can issue certificate.

 

[Sintra]

Yes agree you could end up with a bit of a problem if the circuit you move has a fault on it.

 

[PeteC]

have meeting with management tomorrow so needed to straighten it out in my head

thanks

 

[rryles]

Sorry, but I fail to see the logic in spending over 10 grand on a PV system and them getting tight when it comes to connecting it to the installation.

Don't you need to get new meters installed for the feed in tarrif anyway? Wouldn't that be a good time to get an isolator fitted?

 

[sparks1234]

Technically you shouldn't be cuttting the main tails and installing another consumer unit, the reason being you then do not have the single "main switch" to turn the whole installation, I know this was the way years ago and it has been discussed on this forum previously.

 

[PeteC]

Yes, good point. Can you not interpret it as 2 separate electrical installations though. The method of henley block splitting seems acceptable use in renewable energy installations, and you may find similar, at least on the neutral where a service head supplies multiple separately metered domestic supplies, and the DP isolation required is set after at the mainswitch?

ps.rryles I totally agree

 

[malcolmsanford]

Technically you shouldn't be cuttting the main tails and installing another consumer unit, the reason being you then do not have the single "main switch" to turn the whole installation, I know this was the way years ago and it has been discussed on this forum previously.

Regulation 537.1.4 covers why you can split the meter tails into henley blocks and then supply a new CU.

 

[sparks1234]

Read regulation 537.1.4 again
How do you interprete that as being a licence to split the maintails and feed two consumer units before a single main switch

 

[PeteC]

It refers to "every" installation should be..... where it is not definative to what "installation" determines. ie 2 separate installations = total installation or does it mean all consumer installation after the supply?

This would be a good query to clearup

 

[ezzzekiel]

isolator to henlys to 2x db

 

[sparks1234]

It refers to "every" installation should be..... where it is not definative to what "installation" determines. ie 2 separate installations = total installation or does it mean all consumer installation after the supply?

This would be a good query to clearup

Yep, thats the way I do it, adds the cost of an isolator but at least it complies