Oil boiler, and RCD protection, not sure what to do if anything?

[ericmark]

When the solar panels were fitted, the boiler was taken off the RCBO supply and connected to the new UPS, with no RCD protection, I popped out and got a RCD FCU, however when the boiler fired, it tripped, this was winter, so not the time to mess around, so put the non RCD FCU back.

I noted before the work was done, total earth leakage for house around 26 mA, and after the work was done, around 8 mA, so it does seem likely I have a 18 mA leakage on boiler. No easy point to put my clamp around to measure.

So the question is, do oil boilers 25-year-old leak to earth anyway? Is there something with the ignition system which means it will always lead some current to earth? There is cabling to pumps, motorised valves, and the local room thermostat, but the main room thermostat (Nest Gen 3) is 12 volt SELV so no long cable runs buried in the wall. So inclined to leave it without RCD protection, after all I have a compliance certificate saying all complies. So the only person who could be in danger is the boiler service engineer.

I am undecided, should I look for the earth leakage, or should I simply say not my call, I did not remove the RCD protection so why should I worry, as it is, it's less likely to fail. Fact that old RCBO did not trip, it could be the RCD FCU is too sensitive, my RCD tester died.

Thoughts please.

 

[securespark]

You could swap the RCD FCU for a new one, but you have to trust without test equipment that it is within spec.

Does your son have a working RCD tester?

As it is now a lot drier, I would be tempted to refit RCD protection and see if it trips again.

Can you temporarily alter the wiring so you can get a clamp-on round the cable?

I have come across many oil boilers and some had RCD protection. I see no reason why an oil boiler cannot be protected by an RCD. But these days it should be a Type A.

 

[JohnW2]

So the question is, do oil boilers 25-year-old leak to earth anyway? Is there something with the ignition system which means it will always lead some current to earth?

I have no idea, but if it works by producing a spark 'to earth' then I suppose that would be inevitable, but only during the very brief period whilst the ignition system was 'firing'.

If that were the case, then, although it would be a bit of a hassle, I suppose you could protect it with a time-delayed 30mA RCD (which, perhaps surprisingly, seem to be fairly readily available) - which would be better than no RCD protection?

 

[ericmark]

I will once daughter moves out, look at getting clamp on around cables. It did not trip the RCBO, but did trip the RCD FCU, which seems odd, could find a type A RCD socket, but not FCU, so may change to plug and socket, so can power freezer from it.

But just wondered if there was some thing which causes oil boilers to trip?

Boiler guy coming 12th next month, so need to take insulation tester as clamp on down and see what they show before he arrives.

 

[JohnW2]

I will once daughter moves out, look at getting clamp on around cables. It did not trip the RCBO, but did trip the RCD FCU, which seems odd, could find a type A RCD socket, but not FCU, so may change to plug and socket, so can power freezer from it.

As you know, when one has two or more residual current devices in series, it's essentially pot luck as to which (or how many) will trip when a residual current appears.

I presume that it was/is a 30mA RCD FCU? (there are a good few 10 mA one s around)

But just wondered if there was some thing which causes oil boilers to trip?

As I wrote, it might be an inevitability (during 'firing' of the ignition system), depending upon how the ignition system works. Particularly in the case of your old boiler, it's possible that not enough thought was given to the impact of RCDs back then?

Boiler guy coming 12th next month, so need to take insulation tester as clamp on down and see what they show before he arrives.

I'm not totally sure what that sentence means, but if you;'re saying that you'll have to undertake an IR measurement because your clamp meter is not working ("down"), then that would presumably not detect a issue which only exists whilst the igniter is firing.

 

[ericmark]

No both clamp meter and insulation tester reasonable new. Clamp meter tests AC and insulation tester DC so will use both, so any capacitance or inductive leaking will show up as that.

But when using oil heaters in the past they were not on any RCD protection, so I have no experience on what to expect, so thought worth asking in case oil boilers have some feature making them unsuitable for RCD protection.

 

[JohnW2]

No both clamp meter and insulation tester reasonable new. Clamp meter tests AC and insulation tester DC so will use both, so any capacitance or inductive leaking will show up as that.

Yes, but neither would 'show up' anything during normal testing if the 'leak' were only present for the duration of the spark.

Also, it would require a very large amount of 'capacitive coupling' (I think about 265 pF) to get an 18 mA leak with 230V 50Hz.

But when using oil heaters in the past they were not on any RCD protection, so I have no experience on what to expect, so thought worth asking in case oil boilers have some feature making them unsuitable for RCD protection.

I have no experience of oil boilers at all, but, as I've said, IF the igniter produces a 'spark to earth' then, if the current involved is high enough, they would obviously be "unsuitable for RCD protection" of such equipment.

 

[ericmark]

This is why I have asked, if not suitable, prefer not to fit, rather than have a problem with heating in winter.

I am not sure of wave form, assume sine wave, but nothing on inverter spec to say if there is any problem using a RCD on the supply, two type A sockets feed my freezers, but two of them are inverter drive, so again out of my knowledge as far as any interaction between inverters, but they seem to work OK.

 

[JohnW2]

This is why I have asked, if not suitable, prefer not to fit, rather than have a problem with heating in winter.

Fair enough - but it presumably wouldn't take you more than a few minutes to remove or bypass an RCD should you fit one and then "have a problem in winter" ?

 

[ericmark]

Fair enough - but it presumably wouldn't take you more than a few minutes to remove or bypass an RCD should you fit one and then "have a problem in winter" ?

I have done a risk assessment, and I feel the risk of slipping in snow or ice going to reset and RCD which has tripped is higher than the risk of a shock from no RCD protection, so have abandoned the idea of fitting a RCD in the interests of safety.

 

[JohnW2]

I have done a risk assessment, and I feel the risk of slipping in snow or ice going to reset and RCD which has tripped is higher than the risk of a shock from no RCD protection, so have abandoned the idea of fitting a RCD in the interests of safety.

Very reasonable - but would it be possible to install (in summer!) an RCD in a location that could be reached without possibly having to do battle with snow or ice?

 

[ericmark]

I live on a hill the garage has the consumer unit and central heating boiler in it, with no internal access to main house, the garage has been turned into a flat, so the whole ceiling has been done with plaster board, so we have plaster board, insulation, the original ceiling and then a void and finally floor of main house, which had problems, so is now double thickness with plywood over the original sheets.

The RCD's for the freezers are in the main house, with SWA around outside the house to feed them, all other RCBO's are in the flat, but should one trip, it would not be urgent to reset it, we could survive without any single RCBO, except for central heating, we have an open fire, but to get wood to burn would also mean going outside, and the whole idea of having UPS on the boiler supply was to reduce the chance of the central heating failing even with a gird power failure.

So to fit a RCD seems on reflection counterproductive. I have had a handrail fitted since the picture, but that was because I fell, going down to flat, with a little ice on the steps, so danger of falling is real, danger from electric supply to boiler, seems very low in comparison. On reflection, I was really only fitting a RCD as a precaution against a very low risk.

 

[JohnW2]

.... On reflection, I was really only fitting a RCD as a precaution against a very low risk.

... is that not the case when we install any RCD ? (but that doesn't stop us installing them )

 

[Rodders53]

FWIW my 15-16 year old Grant oil boiler is fed from a RCD protected circuit. Never tripped afaik.
(All circuits in the home are fed from one of two 30mA RCDs.).

Some RFI suppression circuit designs (perhaps of older design?) give earth leakage currents.

 

[JohnW2]

Some RFI suppression circuit designs (perhaps of older design?) give earth leakage currents.

I think that many 'not old' designs still involve capacitors from both L and N to earth - and since the voltage across (hence current through) the L-E one will be much greater than for the N-E one, there will be a significant net L-N imbalance (e.g. as seen by an RCD). Howere, that alone would never be enough imbalance to trip a 30 mA RCD, so would only become a potential issue if there were other 'leakages' on the circuit.