30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is off

[vitoboy]

Hi all
Ok...been to a job today with a random tripping 30mA rcd
its a bit of a full on install...at a undertakers....
3p cutout feeds 3 main switches...1 for a workshop db...for a flat over the undertakers...1 for the undertakers....
from the undertakers mainswitch...we have a swa submain to a db...3 more submains to 3 other dbs..one of which goes to a small garageon the se o the flat.
customer says that when he swtches on flouresent lights (any..connected to any of his 4 db's) sometimes his rcd trips..
ive seen this today...
so...ramp test the rcd...(hager 100A 30mA .....fitted it 18 months ago when the last one tripped to early..!) goes off at 17mA every time.
when I switch off the submain to garage .... it goes out at 23ma..and all is fine.
sub main tests fine...
submain db tests fine..all its cabling tests fine....

turn off submain db circuits one at a time...no difference...still trips at 17mA.......
ill return to the job as I ran out of time.....

ANY THOUGHTS....?? GREATFULY ACCEPTED

can it be just a mass of leaky appliances all contributing...???

let me know..

cheers

vitoboy

 

[TJ Anderson]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

what other tests have you done?

 

[R G]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

What is this RCD covering , is it the 4 DBs that you mention did you RCD test and ramp test at the RCD with no loads connected or main switches isolated ..

 

[Anthony S]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

Not being funny mate, but that write up is all mish mash

 

[Darkwood]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

If the submain is SWA then why has someone designed it with upstream RCD protection - this is poor design and regardless of final conclusion as to why its tripping ...it was waiting to happen taking a whole submain out!

 

[Silly Sausage]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

Hi all
Ok...been to a job today with a random tripping 30mA rcd
its a bit of a full on install...at a undertakers....

ANY THOUGHTS....?? GREATFULY ACCEPTED

Ghosts, obviously.

 

[nickblake]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

I'd start doing a few insulation tests especially neutral to earth

 

[Octopus]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

Hi all

so...ramp test the rcd...(hager 100A 30mA .....fitted it 18 months ago when the last one tripped to early..!) goes off at 17mA every time.
when I switch off the submain to garage .... it goes out at 23ma..and all is fine.

vitoboy

I think your outline of the situation points you to where you need to focus your attention!

 

[telectrix]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

ballast leakage on fluorescents.

 

[Guest125]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

Definitely a problem of some sort....

 

[Deleted member 72666]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

Hi all
Ok...been to a job today with a random tripping 30mA rcd
its a bit of a full on install...at a undertakers....
3p cutout feeds 3 main switches...1 for a workshop db...for a flat over the undertakers...1 for the undertakers....
from the undertakers mainswitch...we have a swa submain to a db...3 more submains to 3 other dbs..one of which goes to a small garageon the se o the flat.
customer says that when he swtches on flouresent lights (any..connected to any of his 4 db's) sometimes his rcd trips..
ive seen this today...
so...ramp test the rcd...(hager 100A 30mA .....fitted it 18 months ago when the last one tripped to early..!) goes off at 17mA every time.
when I switch off the submain to garage .... it goes out at 23ma..and all is fine.
sub main tests fine...
submain db tests fine..all its cabling tests fine....

turn off submain db circuits one at a time...no difference...still trips at 17mA.......
ill return to the job as I ran out of time.....

ANY THOUGHTS....?? GREATFULY ACCEPTED

can it be just a mass of leaky appliances all contributing...???

let me know..

cheers

vitoboy

Are you sure there isn't a flat under the overtakers!

 

[Sintra]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

So you have 23mA with the load (or a part load) disconnected and 17mA with a load on it. That would suggest that there is 6mA leakage acquired through the load. You really need to test the RCD at its terminals with no loads connected and then test for combined leakage from the connected loads. It would also be advisable to do an IR test as previously mentioned.

 

[SPARTYKUS]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

Vitoboy

like MC Hammer, you need to
"Break it down"

 

[vitoboy]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

WOW...for a help forum there are some pushy answers on here....
that's what I get for saying all answers accepted I guess..

but in general....

of course..the sub main to garage is t&e...buried in the wall..hence rcd.
yes ...ive I/r tested it..its all good.
circuits connected to it I/r tested....all good.
system design ....yep...rubbish...but been in place for years..not my work...
are you suggesting a rewire of everything coz of a random tripping rcd...?

leaky flour ballast..yes lots of them..all in different area's...all ok without the garage sub main connected.

I was just hoping for some other ideas apart from....30 appliances leaking making up my 8ish mA leakage.

cheers all for the serious replys among this

vitoboy

 

[Engineer54]

Re: 30mA rcd trips at 17mA when submain connected mcb is on...ok when submain mcb is

Where is this tripping RCD located, at the garage CU or at the origin of the submain to the garage??
Is there 2 or more RCD's in series, eg sub main and CU?? If there is, then the upstream needs to be an S type 100/300mA RCD to give discrimination between the RCD devices.

To locate leakages, you'll need to invest in a earth leakage clamp, which nowadays with almost every installation including RCD devices of one form or another every jobbing electrician should be carrying.