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martinsmit
martinsmit

Posted: Mon Apr 06, 2009 10:07am

Post Subject: CONSUMER UNIT/INVERTER

Hi there again tony. I'm fitting an small consumer unit after my 600 watt inverter. I purchased one from B & Q which came with a 63 amp RCD then i purchased a 6 & 10 amp MCB'S all i have at the moment is three double sockets and a single socket, 240v i've been told by a boat safety inspecter that i need to change the 63 amp RCD down to a 25 amp mean while with regards to the 6 & 10 amp MCB'S he told me that this is the most amps you can have, 16, which i understand, but since i have 12 volt lights i will not need the 6 amp but will need the 10 amp but again i'm a bit confused why 10 amps when i would be using 13 amp fuses in anything 240 could you confirm what is correct. Thanks again for your time and help. regards martin

Tony-B
Tony-B

Posted: Mon Apr 06, 2009 4:38pm

Post Subject: CONSUMER UNIT/INVERTER

Dear Martin, I can not go against a BSS inspector, but I was not aware that the BSS covered the AC circuits. I simply do not understand what he is saying. First of all the RCD. This will have a maximum switching current rating which I assume is the 63 Amps - it has nothing to do with the RCD operation save than the maximum current the unit can switch. The important rating for RCDs is the "out of balance" milliamp required to make it trip when a fault occurs this will almost certainly be 30mA being a UK unit and that is the "standard" for this country. The MCB is doing the same job as a fuse and the important rule for both is that they are rated to protect the CABLE. So if your mains wiring cables are rated at 6 or 10 amps or above then you can use the relevant MCB. Mains are usually wired in a ring that allows two current paths which in turn allows you to draw more current than a single cable can carry (its called diversity if you want to look this up)but I expect your three outlets are just strung along a single cable, so that cable must be capable of carrying at least 10amps. I very much doubt you will be trying to run 3 KW loads (which require 13 amp fuses in the plugs) so absolute best practise would be change the plug fuses to 5 or 10 amps. I would have much rather the examiner had explained the importance of where to connect the hull earth. If the inverter has a three cable output the hull earth bond should be taken from a point BETWEEN the inverter and RCD otherwise the RCD will not work. If the inverter only has a two wire output it is vital to check with the manufacturer/distributor before trying to utilise the neutral cable to form an earth setup. More info on Smartguage webpage. Tony Brooks

martinsmit
martinsmit

Posted: Mon Apr 06, 2009 6:20pm

Post Subject: CONSUMER UNIT/INVERTER

Hi Tony Thanks for the info again. Just to confirm that the chap i speak to a bit works for a hire company and he installed our gas, so that i could get it Gorgi registered he also carries out boat safety as well. With regards to the cable run, your correct it just runs along one side, with no return, thats how the boat builders installed it with the tails left in the electric cupboard ready to connect to an inverter of choice, i will just check what the cable is rated at but i think it is fine as it is, 3 core and blue in colour on the outside, the same that you can get from any chandlerys. As for the inverter it is a sterling inverter charger 600 watt and all i have is coming out of the bottom is the positive and negative leads and on the top is a normal plug socket to connect a cable to from the consumer unit and then the consumer unit to the run of cable to the sockets. What i have done is fitted a isolation switch in the positve line, so it goes from the battery then switch which then goes through a 100 amp fuse and then up into the inverter, is this ok, also does the earth have to be connect to the boat from the consumer unit. Thanks very much again Martin

Tony-B
Tony-B

Posted: Tue Apr 07, 2009 9:33am

Post Subject: CONSUMER UNIT/INVERTER

The fuse in the inverter DC supply should be a close to the masterswith as possible so it protects the maximum amount of the cable run. Without seeing where the "earth" connection in the consumer unit is in relation to the inverter and RCD I am unable to say more about this than I did in my last reply. If you omit an hull earth bond the system will appear to work OK but in the event of a mains short circuit to the hull or other metal part the RCD would not trip, so posing an electrocution hazard. I regret I can not say much more. Tony Brooks

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