Economy 7 RCD tripping.

[DeanoZX7R]

Hi Guys,

An elderly customer has just moved into her new flat, unfortunately her heating on E7 doesn't work. The E7 dist board RCD is tripping (probably as it kicks in).
She has two boards, one normal and one E7. The E7 board is feeding three night storage heaters and an immersion heater. All the wiring checks out fine, the heaters are working (tested). What I find strange is that the neutral tails for both boards are commoned at a Henley block BUT when I tried to jump a feed from the live board, the live board RCD trips. The culprit appears to be when the neutral bus bars of both boards are connected directly to each other. What I can't understand is why, when both neutrals main tails are already commoned?

As for the heaters not working I think a time delay RCD may remedy the tripping. Any ideas greatly appreciated!

 

[Clive P]

Hi,
Sounds to me like a Neutral fault somewhere. Did you operate or bypass the stat for the Immersion prior to testing. I certainly wouldn't be putting a time delayed RCD in, I would be looking to rectify the fault.
Regards.

 

[DeanoZX7R]

Hi Clive,
The time delay RCD is to prevent the storage heaters from tripping the RCD when the E7 kicks in. Each circuit has been tested individually and they all work. The problem arose when I tried to jump a supply from the live board to the E7 board.

 

[Plonker 3]

Have you ramp tested the RCD?

 

[DeanoZX7R]

This is where it gets bizarre....
Ramp tested live board RCD....49mA but didn't trip?
Ramp tested E7 board RCD.... 47mA and did trip. (Obviously using temp supply from live board). Both RCDs 30mA 63A units.

 

[Plonker 3]

Sounds like both RCDs need changing if they are allowing nearly over 50% the amount of leakage. Could be the mechanism inside both of them is shot and therefore not allowing for the inrush of all 3 heaters starting at the same time.

 

[i=p/u]

Contractor no?

 

[Clive P]

Hi,

It's quite common to still run banks of storage heaters off an Economy 7 Board or via contactor using the Meter output as the control circuit. I worked on one the other day which switches a number of heaters. Thing was that wasn't a domestic environment, so no nuisance tripping from RCD's.
As Dillb says your' RCD results aren't satisfactory and definitely need looking at.
Your cross-over supply check, well here you have commonned Neutrals on the supply side which is correct, and possible crossed over on the load side depending on what you had isolated at the time ( before the temporary link ). It can sometimes be difficult to envisage the set up without seeing it.

Regards.