This discussion is locked.

You cannot post a reply to this discussion. If you have a question start a new discussion

Earth Leakage - Boiler?

Called at my friend's house where he is looking to run CAT6 underground today and he was telling me about his RCD tripping problem.

Virtually every day his RCD trips. Single phase overhead TT supply. Single 30mA RCD in Consumer Unit.

The problem started soon after a new oil fired CH boiler was fitted.

Putting a clamp meter around the meter tails, from 21 to 0mA unbalance step by step as the single pole MCBs were opened one by one.

Rather upsetting to find that with all MCBs in and 21mA unbalance there was only 2mA in the earth lead, could not find either the cable connection or the rod outside.

Hoping to find a convenient place on the boiler where I could access the L & N to check unbalance looked inside and nothing accessible within the time I had. Anyway out of "devilment" you could say, put the clamp meter around one of the CH pipes from the boiler and 21 mA flowing through the 22mm pipe! I'm guessing that assuming the cable and rod are ok, the earth leakage current will flow inversely proportional to the respective resistances.

He has been trying to get an Electrician in to sort out.

Besides ensuring a decent earth rod and cable to the MET I think the ideal would be a new Consumer Unit (metal of course) and Cobs.

To try and confirm the boiler being the main cause, since the CH system runs from a nearby 13a socket, have considered a short extension lead where the L, N & E are separated out for easy application of a clamp meter.

Any other checks to try before his Electrician gets in heavy style?

Clive

Parents

0 AncientMariner over 5 years ago

Thanks for all the advice.
MHRestorations
Why I didn't measure the flex for unbalance I don't know. Likely I was watching the time since I needed to get home, change and take myself and my wife elsewhere.
Also, that 21mA through the pipe, was just one of the outgoing pipes, but due a rather tight install, neat really considering that this was a replacement CH boiler, I could not find another suitable pipe.

Whilst I understand the different earthling systems, our two house have both been TN-S although previously my parents farmhouse was TT with fuses - some likely in the Neutral and earthling via the lead water pipe with no ELCB or RCD… My time at sea was with isolated systems with no neutral, the 220v domestic supply being across to phases.

Once the fault at my friends house is found and fixed, I would like to see a new consumer unit with ideally RCBOs rather than one or two RCDs. Is there a requirement for 2-pole RCBOs due it being TT? However, one problem is going to be location for new equipment. It is an old farmhouse with the cut-out and meter in one triangular cupboard and the CU in one next to it. These being directly under the roof at a lowish height - I can just reach the bottom of the CU. In fact until Scottish Power changed the supplied to overhead concentric, he could actually reach the bare overhead supply where it was secured to the porcelain insulator just above the kitchen door! I would also like to see a REC2 between the meter and the CU, but no room in either cupboard. Yes, the earth rod, if there is one needs attention, just wondering whether it is the water supply pipe - will ask him to check.

Mike
Yes a N+L to E check may be revealing. I will dust off my megger. Also a little bit here, a little bit there, it all adds up there must be some current due suppression capacitors - 0.4µF would give 30mA at 240 volt - quite a bit I know for suppression, but it all adds up! Then again the RCD may have gone over sensitive. His electrician can check that.

Andy
The CH boiler and pump are fairly new (months) but could be a rogue one with low insulation resistance.

A N-E fault brings back memories of some years back well before Part P when if you installed new circuits etc you could fill in an Electricity Board form and they would come out, test and connect up.

I fitted a RCD or RCCB as it was called then and left it with new meter tails ready for connection. MANWEB's Engineer came out, pulled the cut-out fuse and connected it in. Problem now was that it would not set! You have a problem he said as he left! He advised that I would soon find it - look in your sockets. Sure enough in one back-box the earth wire had pressed its way through the black insulation of a neutral. A quick rearrangement of the cores and problem gone. It never tripped again for the remaining years that we were there. Chances are that fault had been there for some time just waiting to be revealed.
Yes, a slight expansion of a water pipe may be all that is needed.

Clive
Cancel
Vote Up 0 Vote Down

Cancel

Reply

0 AncientMariner over 5 years ago

Thanks for all the advice.
MHRestorations
Why I didn't measure the flex for unbalance I don't know. Likely I was watching the time since I needed to get home, change and take myself and my wife elsewhere.
Also, that 21mA through the pipe, was just one of the outgoing pipes, but due a rather tight install, neat really considering that this was a replacement CH boiler, I could not find another suitable pipe.

Whilst I understand the different earthling systems, our two house have both been TN-S although previously my parents farmhouse was TT with fuses - some likely in the Neutral and earthling via the lead water pipe with no ELCB or RCD… My time at sea was with isolated systems with no neutral, the 220v domestic supply being across to phases.

Once the fault at my friends house is found and fixed, I would like to see a new consumer unit with ideally RCBOs rather than one or two RCDs. Is there a requirement for 2-pole RCBOs due it being TT? However, one problem is going to be location for new equipment. It is an old farmhouse with the cut-out and meter in one triangular cupboard and the CU in one next to it. These being directly under the roof at a lowish height - I can just reach the bottom of the CU. In fact until Scottish Power changed the supplied to overhead concentric, he could actually reach the bare overhead supply where it was secured to the porcelain insulator just above the kitchen door! I would also like to see a REC2 between the meter and the CU, but no room in either cupboard. Yes, the earth rod, if there is one needs attention, just wondering whether it is the water supply pipe - will ask him to check.

Mike
Yes a N+L to E check may be revealing. I will dust off my megger. Also a little bit here, a little bit there, it all adds up there must be some current due suppression capacitors - 0.4µF would give 30mA at 240 volt - quite a bit I know for suppression, but it all adds up! Then again the RCD may have gone over sensitive. His electrician can check that.

Andy
The CH boiler and pump are fairly new (months) but could be a rogue one with low insulation resistance.

A N-E fault brings back memories of some years back well before Part P when if you installed new circuits etc you could fill in an Electricity Board form and they would come out, test and connect up.

I fitted a RCD or RCCB as it was called then and left it with new meter tails ready for connection. MANWEB's Engineer came out, pulled the cut-out fuse and connected it in. Problem now was that it would not set! You have a problem he said as he left! He advised that I would soon find it - look in your sockets. Sure enough in one back-box the earth wire had pressed its way through the black insulation of a neutral. A quick rearrangement of the cores and problem gone. It never tripped again for the remaining years that we were there. Chances are that fault had been there for some time just waiting to be revealed.
Yes, a slight expansion of a water pipe may be all that is needed.

Clive
Cancel
Vote Up 0 Vote Down

Cancel

Children

No Data

Earth Leakage - Boiler?

Community Rules & Guidelines