Which consumer unit?

[TheKeymeister]

I'm in the process of designing a rewire for the house I'm buying (1950s big ish 3 bed semi) I've split most of the circuits over 2 RCDs (3 circuits on one, 4 on the other) but I have an additional three circuits that I believe should be non RCD protected. Freezer spur, UPS spur and submain to workshop/garage. Always worked with and trusted MK stuff for small power, so had a look at MK Sentry range but from what I can gather most of the twin RCD boards only seem to support 2 unprotected circuits. They claim to be fully flexible and what not, I can only assume the limiting factor is the unprotected neutral bar as you cut the live bar to suit?

Any suggestions on this? Probably obvious to anyone who's opened one before but they're a bit different to the boards I'm used to working on (I'm an ex industrial spark and now work for the DNO). Should I be looking at a different board completely?

I'd love to RCBO everything but my bank balance says differently! The other option I've just thought while writing this would be to wire the freezer and UPS as a radial out of 1 breaker which actually sounds like a decent idea but the red, sorry green, book probably says otherwise somewhere!

Oh and before anyone asks, I fully intent to notify building control etc with regard to these works.

I'd have loved to have just slapped up 20mm galv conduits everywhere but I don;t think the other half would agree!

 

[17thman]

nothing wrong in supplying freezer and UPS on the same radial in terms of electrical safety. if you do require non rcd protected circuits then the installation method is a consideration. ie cannot be buried less than 50mm without earthed 3mm steel protection. That will probably open a can of worms with the more discussive around here.

 

[TheKeymeister]

nothing wrong in supplying freezer and UPS on the same radial in terms of electrical safety. if you do require non rcd protected circuits then the installation method is a consideration. ie cannot be buried less than 50mm without earthed 3mm steel protection. That will probably open a can of worms with the more discussive around here.

Sounds like a brilliant excuse to get the conduit bender out

 

[Iggifer]

take a look at (page 4):

http://www.tlc-direct.co.uk/Technical/DataSheets/MK_Sentry/SENTRY_prod1.pdf

The K5616s can take 8 unprotected ways if I'm reading it correctly.

As I have made no secret of, I am a big, big fan of pushing the boat out for RCBO's. I went with an Eaton all RCBO board, upgraded from a split load MEM board, the quality is top notch, i don't remember the figures off hand but RCD trip times on the RCBO's are in the region of 16ms (with the load connected). In the 6 months it's been in, I've had one trip on a lighting circuit (overload not leakage) compared to a trip a month or so on the split. Eaton board is super easy to wire, the MCB pan is really well designed. They also do an extra height model to give more room for RCBOs

I personally wouldn't use MK, the quality of their CU's & CPD's just isn't as good as other brands, especially given the premium you pay for MK.

It cost me probably just over twice what a split load board would have cost (maybe 2.5 times) but also means I save 4 ways in my CU.

Untitled

• Iggifer
• 16 Dec 2012
• 1

Think it looks better than the MK boards do too

 

[Click4]

They support more than 2 non RCD circuits.

In fact on their largest unit I've done it twice now, 5 unprotected, then 5 on each rcd... 15 ways total.

 

[RF Lighting]

It's not going to cost all that much more to go for an RCBO / MCB filled board rather than a dual split. Don't forget you'll be saving on the purchase price of MCBs and 2no. RCDs of you do go down the RCBO route.

 

[flameport]

A 2 RCD split will always be a compromise, and in the scheme of a full rewire, the additional cost for all RCBOs is tiny.

A decent 12 way board with 7 RCBOs and 3 MCBs can be obtained for well under £200.

There is nothing to be gained from having a separate non-RCD circuit for a freezer.
If the freezer itself goes wrong, it matters not since it's still broken regardless of what circuit it is connected to.
If something else on the circuit goes wrong, you would normally know immediately, as it's typically portable items like kettles, irons and hedgetrimmers causing RCD trips.

 

[TheKeymeister]

Thanks for the replies, I have 'seen the light' and found some much more reasonable prices for some RCBOs so have decided to go down that route.

Regards the freezer socket, I'm pretty sure my current house has it on the kitchen ring and I've had no tripping so omitting that should be OK, reading on here it just seemed to be the 'done thing' to have a non-RCD freezer socket.

I'm sure I'll be back with more questions, but until now I'm happy enough! Just need the keys now so I can chase me out some walls...and I need to talk nice to some jointers at work and see if I can get the cut out moved!