RCD tripping when E7 switches on

[problems]

Firstly i'll point out that i'm the property owner and the installer of the majority of the electrical fittings in the building, including Main & E7 DB's.
now the history lesson... sorry, but it is relevant
property is 230 years old, I have owned it for 42 years. it was semi derelict at purchase, and i completed most of the rebuild including plumbing & electrics. (i'm not formally qualified in either trade)
building was wired to the existing standards (1978) at the time. and i opted to include E7 as the means of heating.
The system was checked and signed off by a qualified engineer, and the 'electricity board' engineer when meter was fitted.
The E7 DB connected to 6 individual points and 6 heaters of varying capacity were fitted. and the system worked well and reliably.
10 years after installation, i opted for a different heating system and the ESH's were removed, and that side of the system became redundant, though DB and points remained.
approximately 3 years ago the meter was changed, and, as far as i was aware, everything worked ok.
had the odd rcd trip over the years, don't you just love rogue tripping!, on 2 occasions traced to slugs in sockets in the conservatory would you believe... also damp in a JB .... apart from that no probs.

a month ago She Who Must Be Obeyed, decreed that we should have an ESH in the living room and another in the dining room (we won't go into the why's and wherefores right now, i'm just the labourer round here )
so.... ordered 2 nice dual input ESH's (Newlec, but Dimplex by another name), and duly fitted them....
i noted that they required a second (peak) supply into a fused DP point, so put them in as well.

connected the whole shebang up, all seemed great, until the next morning when i noted the rcd had tripped overnight., as E7 was still live, i isolated both ESH's and reset the trip, fine , stayed set ok.
switch on either ESH and the rcd trips.

well, seems i've cocked something up, so, check and recheck all ESH connections... all done by the book, and no obvious errors.

next i make up a cable to connect NSH direct to 24hr supply ..... works fine, no tripping, left for 2 hours for heater to warm up... all ok.

ok, the E7 DB is forty years old and running on 20a cartridge fuses and 60a mcb, (none of which are tripping by the way), so i fit a nice new DB with 100a mcb and 6 20a mcb's ... it would have had to be changed sooner or later anyway.

and we still have the rcd tripping! ....

nothing else, just the main rcd, and if the mcb's for each ESH are isolated then all is ok... and that is just removing live from the circuit, so what can be causing the problem? .... the only thing that has changed from when the old ESH's were removed to when the new ones were installed is the METER ...

going to need some help here guys....

 

[westward10]

Can you show a picture of the internal connections you have made.

 

[Wilko]

Hi - without the benefit of a wiring diagram or pic, I’m going for a guess that when you’ve recently added the peak supply it has resulted in a second path, a shared N effectively. Some of the current (from the circuit with the tripping RCD) now has another path back to the N bar that bypasses the RCD.

 

[MJPD29]

As above with wilkos answer

 

[Lucien Nunes]

As above, it sounds like there is an interconnection or borrowed neutral between the E7 and 24h feeds to the heater, resulting in current from one line returning to the other neutral.

Do I understand correctly the two feeds are still from separate DB's? If so, there is a potentially hazardous situation at the moment of one DB back-feeding the other through the interconnection in the heater, so one DB and all circuits connected to it might still be live (both L & N w.r.t earth) when its main switch is off and none of the connected loads are operational. Therefore I would isolate both DBs / heaters and at once until the two feeds to each heater can be proven electrically separate.

 

[suffolkspark]

those dimplex heaters have seperate neutral terminals, you possibly have the on peak neutral in the 9ff peak terminal

 

[problems]

thanks for your replies, the only thing that has changed since the old heaters came out is the meter, and looking at the neutral path both DB's neutrals go to a common JB (i.e. the incoming neutral, neutral to main DB and neutral to E7 all on the same bus. and my thinking is.... if it was a neutral issue, then the trip would still pop once the offending mcb was switched off?
i have double checked the connection (probably treble checked) on the heaters as you are correct, there is no difference between the 24hr connection and the E7 connection, and legends are small and almost unreadable when kneeling down and peering in the side, but i'm confident that they are correct.... (even i can't get them both wrong)... and the heaters are up and active with the 24hr connection on.
yes, i'll upload some pics just as soon as i work out how to do it .

as i'm an amateur, i have contacted a proper electrical engineer who has all the proper tools and knowledge, who will visit me on monday..

i'm sure there is no backfeed path, the connections at the heater are correct and separate.
(one presumes that dimplex would not strap them together ).

also, with the 24hr connection off (dp fused switched outlet), the heaters will still trip the rcd....

but not if i do a temp connection to the 24hr side.

as i said, i'm no expert, and certainly bow to the collective wisdom of you guys on here, but this (to my simple mind) is not rocket science, there is a simple answer just waiting to be hit upon. with the correct equipment and experience.

my thinking is .... meter is only thing to have been changed ... but connections look ok
rcd may be too sensitive, it's 30 years old .. but then why doesn't it trip when heaters wired to 24hr circuit ......

i have spent the last 50 years repairing computers and networks, so fault finding techniques are not alien to me (remember 'divide and rule')... so i'm pretty sure i have done as much as i can without proper test equipment.

 

[marconi]

..

 

[dmxtothemax]

what about a leakage in the water heater element ?
elements are famous for leakage.

 

[problems]

what about a leakage in the water heater element ?
elements are famous for leakage.

erm..... not relevant is it, A) it's not in use and isolated by a DP switched,fused outlet. B) nothing to do with the new installation which is on the E7 DB.

 

[problems]

this morning, whilst E7 was live, i isolated the 24hr feed to the heaters (by switching off at the DP switched outlet), then switched on the E7 DP sw to each ESH. as soon as i tried to make the mcb for either heater the rcd tripped.

just saying

 

[marconi]

How many rcds do you have? My reading of your posts is just one 'up front'.

If it is one up front could you jot down and post what it says on the label on it? Or post a photo of it. Does it look like the attached image - a voltage operated earth leakage circuit breaker which are superseded these days by a current operated elcb.

Is your home earthed by a rod in the ground?

If you are having difficulty taking photos to post, ask a neighbour's teenager to pop round with their mobile phone and take some for you, and then send them to you by email for you to to use.

 

[Deleted account]

More info on the RCD please. where is it located and what is it protecting? Do you have more than one?

photos would be good

edit: beat me to it marconi..

 

[marconi]

Paignton pete re your #11 - nice to know I was thinking along the same lines as an expert electrician.

 

[Deleted account]

Paignton pete re your #11 - nice to know I was thinking along the same lines as an expert electrician.

ive been called a lot of things over the years. “Expert electrician” that’s a first.