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Old 09-20-2007, 03:50 AM   #1
Alex
 
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Can a shower be connected to this?


Guys,

My friend (lives in a pub) has 2 CUs one protected by an RCCB, the other non-RCCB protected. On the RCCB protected CU, the RCCB is 80A 30mA. The MCBs total around 260A in this unit. He wants to add a 40A MCB for a shower. If, having considered diversity, the load is in excess of 40A:
Can the new 40A still be inserted?
Is the only consequence nuisance tripping?
Are there any other EASY solutions?
Thanks,
Alex

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Old 09-20-2007, 10:19 AM   #2
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Can a shower be connected to this?


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Originally Posted by xAlex View Post
Guys,

My friend (lives in a pub) has 2 CUs one protected by an RCCB, the other non-RCCB protected. On the RCCB protected CU, the RCCB is 80A 30mA. The MCBs total around 260A in this unit. He wants to add a 40A MCB for a shower. If, having considered diversity, the load is in excess of 40A:
Can the new 40A still be inserted?
Is the only consequence nuisance tripping?
Are there any other EASY solutions?
Thanks,
Alex
Hi Alex. In what country are you? What is a 'CU'?

Generally, adding the circuit breaker current ratings will not indicate the 'maximum demand'.

Also, since he lives in a pub, it is highly unlikely that he will be able to modify his power distribution board, unless he has the specific permission from the owner of the premises.

Assuming that he does has permission to make such modifications, the size of the service that supplies his unit is needed. (E.g. it may be a 100 Amp service). If the 'maximum demand' is exceeded by adding a new appliance, the upstream circuit breaker on the Main Distribution Board (the MCB that protects the cable, which then supplies his sub-distribution board) could trip due to overload.

Just so we understand each other, an MCB is a Miniature Circuit Breaker & a distribution board is a 'breaker box'. The Main Distribution Board is the box that the main supply connects to for the whole establishment. Any breaker boxes that are installed downstream from this can be called 'sub' distribution boards or 'sub' breaker boxes.

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Old 09-20-2007, 11:50 AM   #3
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Can a shower be connected to this?


Well your not in the USA thats for sure. I would also add that I am not qualified to give advice for your systems. I base my answers on these sites....so use caution I could be wrong. Someone else may be able to correct any of my misunderstandings.
http://www.cse-distributors.co.uk/cable/WiringSupp.pdf
http://download.hager.com/hagergroup...itBrochure.pdf
Ok lets see if I understand what you have . You have two consumer units (CU's) One has has a RCCB that is protecting all the other branch circuit breakers in that CU at 80 amps and 30 ma ground fault leakage. So the answer to your question is... if your diversity load on that CU is calculated at 40 amps before you put in the breaker for the other load for the device /shower and that added load is going to operate at 40 amps then yes you have reached the maximum rating of the RCCB considering diversity. So tripping will be a high possibility but I wouldn't call it nuisance tripping it is overload tripping... big difference. Generally you never want to operate a breaker in the USA at maximum amperage continuously.

You can put in a higher rated RCCB if the "service" MB will allow it and the feeder to the CU will allow it and the rating of the CU will allow it. What I mean by this is if the CU's are fed by remote main breakers or if the main breaker for the CU is located in the CU itself and the MB would become the lesser of the two (RCCB vs MB) after you installed a higher rated RCCB your going to cause the MB to trip if added loads exceed its rating in the future.

I have a question..how are the branch circuit breakers energized after the main? Is there some kind of bus that connects them to the RCCB or Main that you install ? The diagram appears to just be a mounting rail not an energized bus.


Stubbie

Last edited by Stubbie; 09-20-2007 at 02:13 PM. Reason: added "service"
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Old 09-20-2007, 05:06 PM   #4
Alex
 
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Can a shower be connected to this?


Thank you both for the response. I'm in the UK. I did not realise I had posted on a US wbsite. Despite this, you have understood the situation correctly and advised accordingly. Yes the MCB;s are energised through a rail.
It seems like I cannot solve this issue. I am taking an advanced (level 3 City & Guilds), electrotechnical certificate over here but I don't have much practical experience and I don't want to mess around with the meter-tails going into the consumer unit as there is no method of isolation (without taking out the main fuse which only the Electricity Supplier is allowed to do).
Thanks again.

Alex
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