Earth Leakage Detector

[TheBinarySheep]

We have a treadmill that keeps tripping off the RCD when plugged in in the garage, but it doesn't trip of the RCD when connected to a plug in the house (via an extension). The garage and the downsides sockets in the house have their own RCD's.

We've recently had an electrician out who was fitting solar panels for us, who said the issue is likely an earth leakage.

I want to measure the any earth leakage on the treadmill to try and track down the problem, and wondered if this device would do it?

http://www.ebay.co.uk/itm/UNI-T-UT2...711697?hash=item43edb29191:g:uKUAAOSw3mpXIC~2

The device in the link above seems cheaper than the other items I'm seeing, so I don't know if this is the sort of thing I need? My thinking it so create a small extension cable with the earth cable separated from the live and neutral so I can clamp the above device around it.

I've tried disconnecting everything from the garage and only having the treadmill connected, and it still trips the RCD (which is 32amps).

Personally I think there's a problem with the underground cable from the house to the garage, but I'd like to confirm any leakage on the treadmill.

 

[endecotp]

If the problem were with the buried cable it would be expected to trip whether or not the treadmill were in use.

You need to measure the insulation resistance, i.e. the resistance between live and/or neutral and earth.
If I were you I'd start by measuring that with a normal miltimeter. But often the insulation only leaks when a higher voltage is applied, and to test that you need a high voltage insulation test meter - commonly called "meggers" by electricians after the best-lnown brand. You can also find cheap versions on ebay; I've no idea if they are any good.

The meter you've linked to might he able to measure a leakage current, but it's not the normal approach.

 

[Jadele]

I would doubt that the meter linked could measure low enough. We are talking milliamps to trip an RCD (30 usually). Are there any outside lights or junction boxes which may have water in them? The problem is usually that there will be a certain amount of leakage on the garage circuits anyway say 20mA (which shouldn't be there but is not enough to trip the RCD) and then when the treadmill turns on it adds enough leakage to pass the 30mA threshold of the RCD and it trips. The original leakage could be caused by water ingress to outside lights or sockets or even condensation in the garage sockets especially if metal clad ones are in use. There could also be a few other explanations, including as mentioned above the cable insulation being compromised. This could be serious damage or something simple like the earth wire being crushed against another conductor behind a socket or light switch. Other options could be incorrect wiring or a faulty RCD.

 

[TheBinarySheep]

I have one of these? Any use?

https://secure.transtronics.com/M300.htm

 

[TheBinarySheep]

I would doubt that the meter linked could measure low enough. We are talking milliamps to trip an RCD (30 usually). Are there any outside lights or junction boxes which may have water in them? The problem is usually that there will be a certain amount of leakage on the garage circuits anyway say 20mA (which shouldn't be there but is not enough to trip the RCD) and then when the treadmill turns on it adds enough leakage to pass the 30mA threshold of the RCD and it trips. The original leakage could be caused by water ingress to outside lights or sockets or even condensation in the garage sockets especially if metal clad ones are in use. There could also be a few other explanations, including as mentioned above the cable insulation being compromised. This could be serious damage or something simple like the earth wire being crushed against another conductor behind a socket.

There are no external lights connected to the garage circuit. The underground cabling though was probably fitted in the 1970's when the house was built, could it simple be that the insulation has perished? The garage cabling may have been changed more recently, but with it being underground I'm not sure.

We had a garage extension about 3 year ago and joins the house to the garage, so it would be pretty easy to disconnect to the existing garage cabling and route a new cable to the garage from the extension. In fact, there's a socket on a wall in the extension which is essentially the rear of the garage wall too, so simply taking the socket off and drilling through would provide access for a cable into the garage.

 

[Jadele]

There are no external lights connected to the garage circuit. The underground cabling though was probably fitted in the 1970's when the house was built, could it simple be that the insulation has perished? The garage cabling may have been changed more recently, but with it being underground I'm not sure.

It could be.... do you know what type of cable was fitted? Was it done well with armored cable? If you have unplugged everything in the garage and no outside lights or junction boxes exist and you have brought all the sockets forward to check for damage then there is not much you can really test without a speciallist Multi Function Meter. Would be easier to get some one in to test it

 

[JohnD]

I was thinking metal treadmill on a damp concrete garage floor.

Show us your consumer unit, open, please, and indicate which device trips.

1970's cable is pretty sure to be PVC which doesn't perish, though it might have been nibbled by rodents.

You could measure leakage on the treadmill using a PAT tester. AFAIK they are still a few £hundred to buy, but many electricians will know someone who does PATing.

It is a tedious, low-skill job.

You might pick up an older instrument, out of calibration, cheaply.

 

[TheBinarySheep]

How would the treadmill on a damp floor affect things?
I can get a picture of the consumer unit, however I don't know how much help it will be as I believe the cable from the consumer has been replaced up to the point where it needs to go outside where its connected via one of those circular connector blocks to the external cable.

I'm also pretty sure the cabling underground isn't armoured. It's an ex-council house built in the 70's.

 

[Jadele]

it shouldnt really but it could contribute to condensation within the treadmill. Does the RCD trip right away or after a bit of use? When the belt gets going on a treadmill it will generate quite a bit of static which may be the cause of the trip but generally it would trip the house sockets too if it was an excessive fault, which still points then to a fault on the garage sockets circuit. All this assumes you definatley do have two RCDs and one is protecting the garage circuit and the other the downstairs sockets

 

[TheBinarySheep]

it shouldnt really but it could contribute to condensation within the treadmill. Does the RCD trip right away or after a bit of use? When the belt gets going on a treadmill it will generate quite a bit of static which may be the cause of the trip but generally it would trip the house sockets too which still points then to a fault on the garage sockets. All this assumes you definatley do have two RCDs and one is protecting the garage circuit and the other the downstairs sockets

Yes the treadmill can be running for 5 minutes or so before it trips. In our consumer unit we have an RCD for upstairs sockets, RCD for downstairs sockets and one for the garage.

 

[Jadele]

Yes the treadmill can be running for 5 minutes or so before it trips. In our consumer unit we have an RCD for upstairs sockets, RCD for downstairs sockets and one for the garage.

would be good to see a picture of that

 

[JohnD]

circular connector block

Could it be damp?

 

[TheBinarySheep]

would be good to see a picture of that

The garage RCD is the one on the right.

 

[endecotp]

I have one of these? Any use?

https://secure.transtronics.com/M300.htm

It's hard to read in the photo, but I think it has a 2 Mohm range. It's worth trying. Unplug the treadmill, wait a few minutes in case there are any capacitors inside that need to discharge, and measure between earth and live, and between earth a neutral, on the pins of the plug.

 

[endecotp]

That's an "MCB-RCD combination" aka RCBO, so it's conceivable that it's an over-current fault rather than earth leakage.