New build site RCD issues

[ScottishGasMan]

Visit to a new build site today for a couple of boilers tripping electrics (RCD)

New Dual RCD Consumer units, the odd thing is though they trip very intermittently and also they sometimes trip the opposite RCD,



ie on the first property, The heating circuit is on RCD 2, but when turning on fused spur to boiler RCD1 Trips.

On second property it can be alternate, sometimes RCD1 trips, sometimes 2 (with heating load supposed to be on it) and sometimes both. This is with all other MCBs turned off. (also found on pressing test button or RCD1 nothing happens/stays on and powered)



When the wrong RCD for the boiler trips, it does not cut the power to the boiler and it continues to run as normal.

Took a few photos of the consumer units. Remember reading before about neutrals or circuits joined between the 2 causing similar issues. But wanted to get rough idea what's causing it to explain to site agent as it will just be a case of site electrician goes out and blames boiler again.

 

[JohnW2]

ie on the first property, The heating circuit is on RCD 2, but when turning on fused spur to boiler RCD1 Trips.

Do you mean that always happens? If so, neutral probably in wroing neutral bar in CU.

On second property it can be alternate, sometimes RCD1 trips, sometimes 2 (with heating load supposed to be on it) and sometimes both. This is with all other MCBs turned off. (also found on pressing test button or RCD1 nothing happens/stays on and powered)

That's more odd, and we would probably need more information. If one of the RCDs sometimes trips when all of the MCBs protected by it are 'off' then, again, one suspects that a neutral is connected to the wrong bar - but that alone would not explain 'variable' behaviour.

Kind Regards, John

 

[plugwash]

Maybe you are already aware of this or it's something you disconnected for testing, but why does there seem to be a brown conductor hanging disconnected in the back of the CU?

 

[flameport]

and also they sometimes trip the opposite RCD,

Most likely is an interconnection between two circuits, one circuit on each of the RCDs. Lighting would be a the first place to look.
If the trip only happens intermittently it's probably because loadings on the circuits are low or zero (presumably no one living there yet). If so, get an electric kettle or four and try plugging those in both upstairs and down, and it will probably trip all the time.

The other option is something horribly wrong with the electricity supply. Very unlikely, but if it's new build then anything is possible.

There should be full test results for all of them - but again as a new build, I expect there will either be none, or some generic made up in the van style of effort instead.

When the wrong RCD for the boiler trips, it does not cut the power to the boiler and it continues to run as normal.

That rules out the boiler as the fault, it's the installation wiring.

 

[AndyPRK]

the fact that the RCD test button does not work should ring alarm bells!

 

[ScottishGasMan]

Thanks guys.

There still being built at the minute so bar a few energy saving bulbs nothings putting a load on the electrics bar the boiler.

I wont be back at the site as my part of job (checking boilers out) is done, but wanted an idea for report I need to send off to try avoid back and forth between us and electricians.

Typical new build sites (or old refurbs for that) up here generally seem to be "fit everything up and turn it on, if it looks good copy and paste readings for reports all the same" certainly that way for the gas side of the paperwork and I doubt most do the full electrical check, considering the number I've seen when there all signed off and all of a sudden faults only seem to magically appear when a customer moves in.

The loose live cable I've no idea, assuming its for a cooker or something thats not wired in yet it was like that when I took the cover off, I dont have electrical certs so while I'd happily fault find all day long on my own property or a friends, I wouldnt interfere with anything on someone elses site.


Does it matter whether the supply or load neutral goes into the top or bottom of the RCD? found it strange that left hand RCD supply is to bottom and load wire out top, and the other way round on the Right RCD?

 

[ScottishGasMan]

 

[ScottishGasMan]

Heating MCB is on the right hand RCD. As you can see, sometimes both tripped, sometimes one/other/none.

 

[flameport]

Does it matter whether the supply or load neutral goes into the top or bottom of the RCD?

Not for most of them. Those Crabtree things are designed that way, the left side RCD takes the L from the concealed busbar and can only be fitted in one specific position so the neutral in has to be at the bottom. The other one has the supply in at the top and out at the bottom, so the neutral in is also on the top.

Hopefully the busbar in that thing is actually split, and the RCDs are installed in the correct places relative to the split.
If not, that would certainly cause some very unusual operation.

 

[ScottishGasMan]

Not for most of them. Those Crabtree things are designed that way, the left side RCD takes the L from the concealed busbar and can only be fitted in one specific position so the neutral in has to be at the bottom. The other one has the supply in at the top and out at the bottom, so the neutral in is also on the top.

Hopefully the busbar in that thing is actually split, and the RCDs are installed in the correct places relative to the split.
If not, that would certainly cause some very unusual operation.

That answers the next question why the two RCDs look different lol

 

[AndyPRK]

Arh, just put on the report both RCD's trip, when boiler switched on.

The neutral wire is probably in the wrong place (though it looks like they routed them well to avoid that)

 

[ericmark]

I am all ears, never seen a split load RCD before, Found on Screwfix but the instructions don't seem to match the RCD, it says two pole but it only seems to have a neutral connection.

 

[flameport]

it says two pole but it only seems to have a neutral connection.

Line connections are on the back as metal tabs which stab into the busbar.

 

[ericmark]

It seems reading the literature I can find there is an isolator, then three slots for RBCO's then the special RCD with the spades you show, then 5 MCB's then next RCD then further 5 MCB's, however it seems the set up we are looking at has only two slots for RCBO's then the RCD so could the split phase RCD be fitted one slot to far to left and could that cause the problem.

Never used one of these so don't know, it's just a thought?

 

[aptsys]

The RCCB is wired incorrectly. One has the neutral from the feed in at the bottom, the other has the feed at the top.