Hi I have been asked to put in a 7 way board 6 16 16 16 16 16 16. Each circuit could pull around 13 amps apart from 6 amp obviously. But the customer wants the whole thing pp. a time clock so I've been to the wholesalers and they have suggested i switch it though 2 24 amp contractors via timeclock is this right?
It’s bad practice to split the load between two switches, contactors or whatever. If one contactor fails the other is then overloaded. Do the job properly. You could use a smaller 3 phase contactor as shown. There’s no reason to switch the neutral.
Can we assume that these 2 X 24amp contactors ( that is a strange rating) are 3/4 pole and are going to be installed after the MCBs on the load side of the CU ?
Then if that is the case you will need a control circuit for the contactor coil(s). Which voltage contactor coil are you going to use 230volt I assume?
So instead of getting a 7 way CU, get an 8 way and on that spare way fit another 6amp MCB which will be your control circuit.
From the CU take a LINE from that 8th MCB/NEUTRAL/CPC to your time clock supply. From the n/o side of the clock take the LINE to A1 on 1st contactor and parallel to A1 on the 2nd and then NEUTRAL to A2 on 1st contactor and parallel again to A2 on 2nd
Each pole of that contactor is capable of taking 24 amps each, so your 7 x 16 amp circuits will be going through 7 poles each capable of taking a 24 amp load, so they are fine
You don't need 2 contactors, just fit an auxiliary block on top and you can control all from 1.
I'm assuming this is for storage heaters. If so, why not just ask the DNO to fit a timeclock to switch the new board?
Finding an auxiliary block that has 3 N/O contacts will take some sourcing ...................normally they are 2 N/0 and 2 N/C, which is probably why 2 were recommended. Plus you need the auxiliary rated 24 amps ( can't get my head round that value) and most auxiliary are for control so that would be something else not exactly of the shelf
4 N/O contacts is not a problem but I take on board that not many aux blocks will carry 16+ amps.
I still maintain get a proper timeswitch. I have a nice 80A unit in my meter box, although I don't have storage heaters any more so it sits there looking pretty.
Additionally, once you start fitting contactors, then the client has an additional "moving part" in their system. A few years down the line as the contacts wear/burn out they will have more expense.
4 N/O contacts is not a problem but I take on board that not many aux blocks will carry 16+ amps.
I still maintain get a proper timeswitch. I have a nice 80A unit in my meter box, although I don't have storage heaters any more so it sits there looking pretty.
G isn't the No 13/14 on an Aux normally what we use to call in them there olden days a "pulse" contact. I remember the dim and distance past when doing these being told that you never connect a load onto it.
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