Discuss does this RCD need replacing in the Electrical Forum area at ElectriciansForums.net

Welcome to ElectriciansForums.net - The American Electrical Advice Forum
Head straight to the main forums to chat by click here:   American Electrical Advice Forum

A

Andystraughan

hi everyone

a second opinion would be appreciated

was called to a house in February as RCD was intermittently tripping. some times 3 times a day sometimes none. during my initial look i discovered when the oven was ran for more then 5 minutes the RCD tripped. my inspection then found a faulty cooker element which was replaced and hey presto no problems any more.

until this morning. same problem.

RCD tripped twice on Monday didn't on Tuesday but did 3 times yesterday. hasn't tripped today either.

i went today for 2 hours today as it was all i could spare. my tests were as followed

starting with a circuit at a time

extension ringmain all meggered clear N - E 299 N - L 299 E - L 299
hot tub supply meggered clear N - E 299 N - L 299 E - L 299
shower meggered clear N - E 299 N - L 299 E - L 299
cooker meggered clear N - E 299 N - L 299 E - L 299

i didn't test 3 circuits as its a big --- 6 bedroom house and didn't want to go around unplugging everything - down ring main - up ring main - kitchen ring main.

i then decided to ramp test the RCD. i disconnected every earth and neutral except the extension sockets which i know are clear. also turned all mcbs off excluding extension(where my megger was plugged into) the RCD tripped at 17mA. the mains RCD is a 30 mA 80 amp crabtree starbreaker split load, i then tested the RCD on half times which tripped the RCD immediately. i tried numerous times. is this RCD faulty? i have more follow up tests to do but don't want to purchase a crabtree RCD without factoring in other causes

like i said i was limited to 2 hours so couldn't do thorough test until next week.

any advice would be helpful

thanks
 
go back and test the RCD with the circuits dissed from it.if it still ramps at 17mA then it's probably faulty. if, on thre other hand, it ramps at say 22mA or over, then you have some leakage on the installation. a mA clamp meter would be useful here. -2
 
I would say that if the RCD has been tripping repeatedly over a long period of time and reset each time then it is probably struggling.
However based on your test results the RCD is faulty, but a test, as Tel says, with no circuits connected would be the clincher.
 
ok thanks i will try with everything disconnected next time. just assumed that as the ring main was clear i could use that to plug my megger into. wasn't 100% sure how to ramp test the RCD as it only has a neutral going through it with it being a starbreaker

thanks for the help
 
With situations like this its best to do FULL rcd tests when investigating and do them each time you visit.

I had one like this a couple of years back and the inconsistent RCD results confirmed that the RCD needed changing - its not tripped since I replaced it.
 
On the flip side there could be a fault on one of the three socket circuits which you didn't get round to testing. I'd do them as well even if the rcd was faulty just for peace of mind if nothing else.
 
wasn't 100% sure how to ramp test the RCD as it only has a neutral going through it with it being a starbreaker

All RCDs require both L & N, you just can't get to the L connections on these when fitted, as they plug into the busbar. Take a load circuit out of an MCB, connect the tester to the MCB terminal and switch only that MCB on.
 
go back and test the RCD with the circuits dissed from it.if it still ramps at 17mA then it's probably faulty.

A 30mA RCD can legitimately operate from anywhere between >15mA and <=30mA. So 17mA is perfectly acceptable.

But I can't understand how the ramp test has shown 17mA and yet we are told 1/2 I delta n trips every time. Is the dial definitely set to 30mA and not, say, 100mA?
 
hi everyone

a second opinion would be appreciated

was called to a house in February as RCD was intermittently tripping. some times 3 times a day sometimes none. during my initial look i discovered when the oven was ran for more then 5 minutes the RCD tripped. my inspection then found a faulty cooker element which was replaced and hey presto no problems any more.

until this morning. same problem.

RCD tripped twice on Monday didn't on Tuesday but did 3 times yesterday. hasn't tripped today either.

i went today for 2 hours today as it was all i could spare. my tests were as followed

starting with a circuit at a time

extension ringmain all meggered clear N - E 299 N - L 299 E - L 299
hot tub supply meggered clear N - E 299 N - L 299 E - L 299
shower meggered clear N - E 299 N - L 299 E - L 299
cooker meggered clear N - E 299 N - L 299 E - L 299

i didn't test 3 circuits as its a big --- 6 bedroom house and didn't want to go around unplugging everything - down ring main - up ring main - kitchen ring main.

i then decided to ramp test the RCD. i disconnected every earth and neutral except the extension sockets which i know are clear. also turned all mcbs off excluding extension(where my megger was plugged into) the RCD tripped at 17mA. the mains RCD is a 30 mA 80 amp crabtree starbreaker split load, i then tested the RCD on half times which tripped the RCD immediately. i tried numerous times. is this RCD faulty? i have more follow up tests to do but don't want to purchase a crabtree RCD without factoring in other causes

like i said i was limited to 2 hours so couldn't do thorough test until next week.

any advice would be helpful

thanks

Why do you want to unplug anything? You are probably looking for a low IR to earth, which is just as likely on a load rather than the circuit. As long as you don't test L-N (which is pointless if the RCD is tripping) and do a soft 250v test initially there is no chance of damaging anything, by disconnecting loads you are removing potential fault sources from your investigations!
 
Why do you want to unplug anything? You are probably looking for a low IR to earth, which is just as likely on a load rather than the circuit. As long as you don't test L-N (which is pointless if the RCD is tripping) and do a soft 250v test initially there is no chance of damaging anything, by disconnecting loads you are removing potential fault sources from
your investigations!

This is why I always to an initial IR test of L+N to earth before unplugging items and then do another one once equipment is unplugged. It helps determine if it's the fixed wiring or an appliance.
 
i checked my store and had an older model crabtree star breaker RCCB. i went back to property to try it out. before i did i disconnected every circuit on RCD side and same test results. ramp test trips at 17mA and the RCD trips at half time on an RCD test. when i swapped over the RCD for the older one the results were as follows

RCD 1/2 - 1999
1 x 34.4
5 x 8.8

ramp test it tripped out at 27mA

i have ordered a replacement RCD so it will be sorted by next week

thanks for the help everyone
 
Once again, how is this possible? Are you sure you have the scale set to 30mA?

A half-current test only utilises 15mA, so if it isn't operating until 17mA then that doesn't make sense.

Mathematically it might not make sense, but it's probably related to the accuracy of the tester.

Mine quotes test current accuracy of -10% to 0% at 0.5I∆n, and 0% to +10% at I∆n and 5I∆n. That suggests that for the 0.5I∆n test, the test current applied by the tester should not be less than 15mA, and may be upto 16.5mA. However, it says that for the ramp test, it increments in steps of 3mA until the device trips. There could well be some ambiguity at where exactly these 3mA steps are. And no doubt, other testers are slightly different.
 
Right. So we are saying that it tests at 14mA, and then at 17mA.

It doesn't actually prove that the operating current was 17mA then but simply >14mA <=17mA.

I never bother with ramp tests except perhaps for trying to find leaky equipment. The standard RCD tests show that the RCD complies with the product standard. Some people seem to think that a 30mA RCD operating at say 18mA is faulty when this is perfectly acceptable and complies with BS EN 61008/61009.
 

Reply to does this RCD need replacing in the Electrical Forum area at ElectriciansForums.net

OFFICIAL SPONSORS

Electrical Goods - Electrical Tools - Brand Names Electrician Courses Green Electrical Goods PCB Way Electrical Goods - Electrical Tools - Brand Names Pushfit Wire Connectors Electric Underfloor Heating Electrician Courses
These Official Forum Sponsors May Provide Discounts to Regular Forum Members - If you would like to sponsor us then CLICK HERE and post a thread with who you are, and we'll send you some stats etc

Electrical Forum

Welcome to the Electrical Forum at ElectriciansForums.net. The friendliest electrical forum online. General electrical questions and answers can be found in the electrical forum.
This website was designed, optimised and is hosted by Untold Media. Operating under the name Untold Media since 2001.
Back
Top
AdBlock Detected

We get it, advertisements are annoying!

Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.

I've Disabled AdBlock