main RCD trips before RCD 30ma spur

[knasher]

just moved in to a new house

fed from 20 amp, Got a 2.5 going to a RCD spur then a 1.5 out of that to a pull cord, then another 1.5 out of that to the shower.

pull cord could be on its way out, does seem to trip when switching, not when in use.

doesn't trip all the time its nuisance tripping.

have used the test button on RCD spur, seems to work ok.

when it does trip, it knocks out the main RCD.

i believe its a 8.5kW

ordering another pull cord but wondering if anyones else has any ideas?

WTF!!! I suppose at least theres some protection with the RCD in there

 

[Hawca]

there a 2 reasons I can think behind why the Main RCD trips before the one on the spur.

1. You will need to carry out a Ramp test on both Main RCD and Spur RCD, this will show at what leakage current both will trip at. You may find that your Main RCD is faulty or over sensitive, or that the RCD spur if not tripping under earth leakage.

2. You may just have a fair amount fo earth leakage on the rest of the installation that when combined with the earth leakage from the Spur cause the Main RCD to trip.

As to the rest of the problems, I recommend you get an inspection done asap. there are a few things not right with either the information you have been given or the installation.

 

[Graeme Harrold]

there a 2 reasons I can think behind why the Main RCD trips before the one on the spur.

1. You will need to carry out a Ramp test on both Main RCD and Spur RCD, this will show at what leakage current both will trip at. You may find that your Main RCD is faulty or over sensitive, or that the RCD spur if not tripping under earth leakage.

2. You may just have a fair amount fo earth leakage on the rest of the installation that when combined with the earth leakage from the Spur cause the Main RCD to trip.

As to the rest of the problems, I recommend you get an inspection done asap. there are a few things not right with either the information you have been given or the installation.

Forget the RCD, look at the cable!!!

 

[Hawca]

Forget the RCD, look at the cable!!!

agreed hence the part where by I recommend the inspection. Wrong information or wrong cable. The initial question was about the RCD.
The problem is with the job.
From this side of my PC screen I cannot tell if the information is correct or misfed information.
What I do know is why RCD's can become a Royal pain in the ---.

 

[morph]

nothing wrong with the cable if it has a 13A fuse

 

[nickblake]

Well reading whats been written , i think there is an error here on info , if its a fused spur on an 8.5kw shower then the fuse would blow simples unless the fuse has loads of fuse wire wrapped round it !!! , i think its more likly to be a power shower 85 watt motor ,might be wrong but it sounds like it to me , but if you are in doubt get it checked by a qualified regestered electrician , reason for the Main RCd tripping would be the tripping current of the RCD will be less than the RCD in the fused spur RCD tripping currents can vary , and will be difficult to test both doing a Ramp test as the main one will always trip first if the tripping current is less than the fused spur , i would remove the RCD fuse spure and install a normal one with the correct fuse rating should be red 3amp for a power shower not 13 amp,, of course if it is an instantaniouse shower at 8.5kw then you have a problem

 

[Des 56]

Is it a power shower

 

[BOROROBBO]

apart from the dodgy 1.5 T&E feeding a shower...... you dont need 2 RCD's on one circuit as it doesnt always say the one closest will trip first

ive had a few jobs where the DP isolator the meter lads put in years ago was one of them old earth leakage things so when i was doing my RCD tests it was that that was tripping before the RCBO in the CU.

 

[Spudnik]

Has anyone thought that it may be a pumped electric shower??

 

[chiplard]

You have a report saying what?? That supplying an 8.5KW shower with a 1.5mm T&E cable is fine?? Well i can assure you it isn't, that 8.5KW shower can draw 37A, and as such i'm wondering how a 13A fuse in a spur can pass that sort of current without blowing???

That shower requires a 6mm cable, so i would be contacting an electrician pronto to make your shower circuit safe for your family....

EDIT... You can think yourself lucky, that spur RCD tripping, may have saved your house from a fire, I'd also check if someone hasn't defeated the fuse in that spur unit, because for the life of me i can't see how a 13A fuse will allow 37A to pass without blowing!!!

Do you not mean a 10mm cable?

A 6mm cable will be working at its limits unless clipped direct. The 10mm will give you more scope with regards to the install method and also allow upgrades of the shower in future.

 

[nickblake]

Has anyone thought that it may be a pumped electric shower??

Me well ish thought it may be a power shower

 

[morph]

10mm is a bit ott, 6 mm is fine infact so is 1.5mm

Do you not mean a 10mm cable?

A 6mm cable will be working at its limits unless clipped direct. The 10mm will give you more scope with regards to the install method and also allow upgrades of the shower in future.

 

[mogga]

nothing wrong with the cable if it has a 13A fuse

13a on a 1.5mm cable feeding an 8.5Kw Shower???? Your havin a girraffee if you think thats "nothing wrong"

 

[morph]

the cable is ok though
i seriously doubt that it is a 8.5 kw with or a fused connection unit , else it would be popping. or they only have very luke warm showers for short periods of time

 

[Des 56]

With the household Rcd tripping and the spur Rcd staying in,it would suggest that.
1 there is earth leakage on that circuit
2 the Rcd is probably correctly functioning, because other applied loads would also affect the Rcd the same

If its tripping mainly when switched on,it may likely be damp tracking in the motor when its standing unused
Whilst in use, the damp tracking may not be as prominent, so less leakage and the Rcd stays in

Dis connecting the pump and re energising with the cable ends made safe may give an indication of where the fault is occuring

I understand you do not have test equipment,because with the correct test equipment, this would be a relatively simple fault to diagnose