Sub-main set up

[viewer]

Wouldn't it be easier to go meter - Henley - 3 switch fuses - protection in each CU? As N & E are not connected, the RCDs shouldn't trip if one detects a problem. Have I missed something?

 

[EFLImpudence]

As N & E are not connected, the RCDs shouldn't trip if one detects a problem. Have I missed something?

Not exactly sure what you mean but if different RCDs share the same Line and Neutral they could all trip.

It's not dependent on the cpc/earth conductor.

 

[viewer]

Ah, yes I was thinking that a fault producing a current in the CPC on a submain of TT system would not trip a RCD on another sub main as the neutrals would be separated from the earth back to the transformer. Any one RCDs would not "notice" a change in the L-N currents for the others as they would be effectively downstream. A bit of faulty logic there!

 

[EFLImpudence]

The ones downstream of an earth fault would not trip.

However, as in the original set up with all sub-mains via the house RCD and MCB, an earth fault anywhere would also trip the house RCD.

 

[SimonH2]

Wouldn't it be easier to go meter - Henley - 3 switch fuses - protection in each CU?

That's about what's suggested - with a couple of issues :
1) I don't know if his layout lends itself to the park home having it's own supply - if it's any distance between house and garage then it could add significant extra cable.
2) If you put the RCD protection in the CUs, then is the submain cable adequately protected ? Ie, is there a need for an upstream RCD just to protect the submain cable, with time delay to discriminate with the "normal" RCD in the CUs.

 

[viewer]

Sub mains each protected by a switch fuse rather than RCD would be simpler and cheaper. No need to worry about discrimination in RCDs. Cost benefit of a separate supply to distant garage / park home has to be based on site measurements, need for excavation etc so cable cost would be one (though not insignificant) factor.

 

[Davisss]

Hi guys. Just an update. I have costed the job based on a time delayed rcd and a switch fuse for each location all fed from the mains position. I think that would be the best solution. Its slightly different logistically than the original plan. Just need to present it to the customer. Thanks for the assistance. Several heads are always better than one!