Calling Adam! LoadCentre Square D consumer unit - 3 phase

I'm not sure if something like this would be considered a "consumer unit"!
There aren't enough ways so considering having a short cable between this to 2 or 3 consumer consumer units, one for each phase.
Currently there is also no RCD protection for socket outlets, so these circuits would be transferred to the new consumer units.
Would 2/3 C63A MCBs in the Loadcentre offer sufficient differentiation to MCBs / RCBOs in the new consumer units? These would be of the Type B variety.
Any other suggestions?
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It depends if you need the Loadcenter for any reason other than powering the CUs!
There is just the simple option of just feeding each CU directly from different phases from the cut out fuses and using a Henley block for the neutral tails.
If the idea of using the Loadcentre is for isolation of the CUs then you might be better off using a 6 way CU/DIN rail enclosure with three 100A DP switches in it - or maybe three Wylex REC2 DP isolators (or similar).
BTW Schneider now own Sqaure D - so is this old/already installed stock you are looking at?
As for discriminaton - there is no point in asking me to say what will trip first. I have seen shorts on a B6 lighting circuit take out both the 63A head end MCB (not my job I would have used a fuse at the head end) and the 6A MCB.
--
Adam


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Yes, there is no discrimination between daisy-chained MCBs for fault current trips (short circuits). The only way the head-end one can't trip is if the short circuit happens a long way down a cable length so the fault current is less than the head-end's fault current trip rating, and in practice this will also mean there's a large difference in the tipping currents of the two breakers.
I was looking to do something like this with a supply to a shed with its own CU. Without using BS1361 CU fuse in the head-end CU, it was impossible, and BS1361 has been canceled, so no one sells the CU fuse holders anymore. I could still use a rewirable fuse, I suppose, sigh.
--
Andrew Gabriel
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On 16/02/2015 20:20, Andrew Gabriel wrote:

As per my earlier reply, I had thought there might be sufficient discrimination between the different types (B, C and D) of MCB. It seems I am wrong!
I suppose there is enough mechanical inertia within each MCB that the higher rated MCB will still break sometime after the fault current has cleared!
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B, C, and D just indicate what the fault current trip rating is, as a multiple of the marked rating.
A C63 MCB has a fault current trip of 10 x 63A = 630A, and. A B32 MCB has a fault current trip of 5 x 32A = 160A.
If you, say, short-circuit a ring circuit on a B32 MCB at a point where the supply impedance is no more than 0.38 ohms (i.e. the fault current will be at least 630A), then both breakers will trip in the same time - the fault current trip time does not depend on by how much the fault current trip rating was exceeded.
If the ring circuit is a long one and you find a position on the ring far from the CU where the supply impedance is more than 0.38 ohms, then a short circuit there might not trip the C63 breaker.

They both try and break at the same time, and although modern breakers extinguish the resulting contact arc quickly, they will still pass current for long enough after the mechanism trips to ensure they all trip ;-).
Fuses are not so trigger-happy.
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Andrew Gabriel
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On 16/02/2015 20:20, Andrew Gabriel wrote:

The BS 1361 fuses are now in BS 88-3 (harmonised with IEC 60269-3): same sizes and ratings that we know and love(?), including the 63 & 100 A house service fuses - and those aren't going to disappear anytime soon.
For submain distribution it seems that Wylex are still be doing the 108 & 108M switch fuses and fuse carriers - although the prices have gone up quite a bit since I last bought any:
http://www.tlc-direct.co.uk/Products/WY108M.html
You're right though in that the consumer unit size fuse carriers are effectively obsolete - try eBay?
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On 16/02/2015 23:31, Andy Wade wrote:

Yup that is a pain... last time I needed one Hager still did them, but the closest they have now that I can find is:
https://www.tlc-direct.co.uk/Products/CGFS100.html
Which seems like a 'kin expensive way of doing it, not to mention the carrier being two modules wide.
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John.
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Wylex recently upped it prices by 25% presumably to try to get away with being at the lower end of the market.
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On 16/02/2015 19:29, ARW wrote:

The Loadcentre is fully populated with a couple of 3-phase outlets. I wasn't going to remove this in the short term.

The only reason I would like to avoid this solution is down to bottle and my dislike of live working. There is an isolator the customer side of the meter, but this still has the local supplier logo complete with seals. I'm reluctant to break these! Of course, using the Loadcentre can be considered a temporary measure and easy to bypass in the future.

I am aware that this is all very old, but you can still get the MCBs on eBay. I'm guessing it could be 20 years old, with seemingly very little modification over the years.

Aah, I thought one purpose of Type B, C and D MCBs was to provide some discrimination?
Many thanks for your time and trouble.
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You are welcome.
In the real world I would actually not be worried about using 63A MCBs from the SquareD to supply new CUs. It's done all over the country in offices, industrial units etc. How many times do you think that discrimination is going to be needed?
If you are struggling for MCBs then drop me an email and I'll see what I can find at work if you do not object to second hand ones.
--
Adam


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On 17/02/2015 17:37, ARW wrote:

I had sort of come to that conclusion after trying to think how many times in recent years I've known a MCB to operate. I feel getting CUs, each with two RCDs offers the greatest protection of all. Currently there's no residual current device anywhere to be seen, something I dislike.

I much appreciate the offer but I've ordered 3 from eBay.
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