Minimum electrical requirements for a new condensing combi boiler install?

[Stephen H]

Am about to sort out the electrics for the new combi boiler.

Old situation is an immersion switch in airing cupboard fed solely by a

16A MCB and a 30mA 80A RCD.

I propose to remove the old immersion cylinder, feed the new boiler from this original immersion switch location by replacing it with a fused connection spur switch with a fuse carrier to take a 5A fuse. This will also feed two motorised valves. (upstairs and downstairs zones). As far as I can see, there is a 16A MCB and a 30mA RCD at the Consumer Unit.

There is currently an earth wire on the old pipework with earth clamps on the old pipework in the airing cupboard.

I propose to take the earth off the old pipework in airing cupboard (all being cut out) and connected to new earth clamps placed on the following locations:

(a) both in & out pipes of both zone valves in airing cupboard (b) run a new earth wire to new clamps on the cold feed, hot water pipe, central heating flow, central heating return and the gas supply pipe at the boiler.

Is this sufficient for meeting all the regulations?

Regards,

Stephen.

[A.Lee]

I think you'll find that a 3A fuse is the recomended size, but other than that, yes, that will be fine.

You probably do not need all of this supplementary bonding. If you have main protective bonding to both gas and water incomers (back to your Main Earthing Terminal, or Consumer Unit), and, all circuits are RCD protected, then there is no need to cross bond any of the pipework, unless the boiler manufacturer says so in the install instructions.

Alan.

[Stephen H]

Thank you for a fast reply, it is much appreciated.

I have however a split load CU.

The two lighting circuits are on 6A MCBs and no RCD protection.

There are four more circuits on a 80A RCD, which is the downstairs ring main, upstairs ring main, cooker and immersion. The first three are 32A MCB's and as stated earlier the immersion is on a 16A MCB.

So will I need the supplementary bonding considering that the two lighting circuits are not RCD protected? If its helpful, there is also two shaver sockets on the upstairs lighting circuit,

Stephen.

[A.Lee]

No, you should not need supplementary bonding for your boiler, unless the boiler maker specifies it, or, if it is in a bathroom, or other special location, and all circuits are not RCD protected.

The gas and water should already be connected to the MET by the Main Protective Bonding Conductors, so all you would be doing is to connect them together at the boiler end, which has already been done when you connect the pipes to the boiler by their copper pipes.

If it makes you feel better, then do it, or, to ease your mind, get a good ohmmeter, and see if there is a good connection from the pipe at the boiler to the MET, - less then 0.05 ohms is acceptable.

Alan.

[Stephen H]

The booiler is going into the kitchen and as I understand it, this is a special location. Only two circuits from the Consumer unit are NOT RCD protected, these are the downstairs and the upstairs lighting circuits.....

So given the above, your final word on supplementary bonding is..... ?

Stephen

[A.Lee]

.........................................should be ARE RCD protected,

No need. It isnt a special location in the wiring regs, it is when concerned with the Buildings Reg. part P. If your gas and water are connected to the MET (by 10mm cable), then it is fine.

Alan.

[ARWadsworth]

If the airing cupboard and it's bonded pipework is currently used to supply the supplementary bonding in your bathroom then the bonding will need to be replaced (just in the way you suggested in your first post).

If the supplementary bonding for your bathroom is OK without the earth clamps in the airing cupboard then you have no problems complying with the regs if you do not replace them.