Long lead appliances and extensions testing and limits.

[ericmark]

The normal long lead vacuum cleaner and lawn mower is no problem as class II equipment but did some testing in a school where I found some projectors, vacuum cleaners and extension leads which were class I as purely due to length of lead they should fail. In my house not a problem all sockets RCD protected but non protected in the school.

For the extension leads RCD plugs were fitted with them I considered even a 1 ohm as being a pass. But I ended up failing the vacuum cleaners and old projectors as double the permitted even though common sense tells me really no problem.

The other problem was some monitors although class I the only metal showing was the plug which would connect to the PC so there was the resistance of supply lead and computer connection lead so again double the permitted resistance which these I passed them as sure if I opened case to get connection they would pass.

I was rather surprised to find no RCD protection in the school and for the extension leads I noted the disconnection time on the paperwork. But should they buy more RCD plugs and fit to the projectors and vacuum cleaners without opening the units it would be impossible to test the RCD plugs other than the test button.

What do others on here do with RCD plugs on other than extension leads when PAT testing? Do you just use test button or do you open appliance to be able to test with meter.

 

[ricicle]

We always used to work to a rule of thumb (or maybe it was guidance from somewhere) that all 230/240v extension leads over 3m or appliances with flexes over 3m had to have RCD protection.
This was especially necessary in our older factory installation where socket circuits didn't always have RCD protection. Where newer/upgraded installs are having the RCD protection at source the need for RCD plugs is becoming less.

 

[Grizzly]

But I ended up failing the vacuum cleaners and old projectors as double the permitted even though common sense tells me really no problem.

The other problem was some monitors although class I the only metal showing was the plug which would connect to the PC so there was the resistance of supply lead and computer connection lead so again double the permitted resistance...

Out of interest, what are you taking as the 'permitted resistance' in these instances?

 

[Spark123]

Our rules do not allow RCDs incorporated into plugs or leads as it makes testing them by normal PAT means impossible.
I'd recommend they get the schools electrical inspection carried out ASAP and they act upon the recommendations.

 

[ericmark]

I took 0.1 ohms as the limit. In most cases this was OK. Only vacuum cleaners, old projectors and long extensions were a problem. I had two machines plus a full test set including a RCD tester so testing the RCD on an extension was no problem. However although I could open up either the plug or machine to test the RCD the idea was once tested then some one only trained to PAT test would follow.

I am uneasy about asking an instructed person to open live equipment for testing.

The other problem is equipment which is built into the framework of the building. Overhead projectors, toilet hand driers, and roller shutter doors. They were not in my remit but neither are they in the remit of people doing the installation testing.

In an ideal world the school should have RCD protection on all sockets but this is not the case and unlikely to be done any time soon.

I had considered using the loop impedance tester for the host of extension leads used. I would take 4 ohms as limit as being the value that will rupture a 13A fuse within the required time. However those following would not have a loop impedance meter and also felt removing the leads and replacing them gave more option to find visible errors on the lead. Also where extension leads are moved around the loop test would become invalid.

 

[Spark123]

How do you IR test with an RCD plug?

 

[ericmark]

How do you IR test with an RCD plug?

Since the IR test was done before I fitted plug it did not really come up. However we do IR tests with RCD's fitted in boards so no really reason why can't be done with a plug.

 

[Grizzly]

I took 0.1 ohms as the limit.

So why not use the actual pass limit, as specified in the code of practice?

(0.1+R) Ω, where R is the resistance of the protective conductor of the supply cord.

Sounds like you may possibly have failed your vacuum cleaners and projectors under false pretenses.

As for testing an appliance fitted with a portable RCD (BS 7071), you wouldn't perform an IR test, as it cannot satisfactorily be performed, due to the RCD only resetting in presence of normal mains voltage.
In these instances, one would do a protective conductor current (aka leakage) test, which are for use if

the insulation test cannot be performed or gives suspect results

 

[JohnW2]

So why not use the actual pass limit, as specified in the code of practice?

(0.1+R) Ω, where R is the resistance of the protective conductor of the supply cord.

Sounds like you may possibly have failed your vacuum cleaners and projectors under false pretenses.

Quite. It was always my understanding that the intent of this test was not to fail appliances because they had long leads but, rather, to fail them if the resistance of the earth fault path exceeded that which could be explained by the cable's CPC (e.g. because of poor connections) by more than a small (0.1&#937 amount. That makes sense to me.

Kind Regards, John

 

[ericmark]

In my old copy of the code of practice it states:-

If extension lead lengths do exceed the above, they shall be protected by a 30 mA RCD manufactured to BS 7071.

Also under schools it states:-

(+) By supervisor/teacher/member of staff
# 110 V earthed centre tapped supply. 230 V portable or hand-held equipment must be supplied via a 30 mA RCD and inspections and tests carried out more frequently. The information on suggested initial frequencies given above is more detailed and specific than HSE guidance, but is not considered to be inconsistent with it.

Having re-read think the # means construction sites but with copy I have not very plain. I have to admit now I have found copy it does state:-

The test current should be within the range 20 to 200 mA.

for 'soft test' I thought same as BS7671 and was 200 mA.

The resistance shall not exceed the following:
(0.1 + R) ohm where R is the resistance of the protective conductor of the supply cord, and 0.1 ohm for appliances without a supply cord.

So it seems I have made an error. Glad I posted as I was not aware had this not been raised here. I had followed the markings of the tester and although with my personal tester analogue readings so I could allow for lead with the schools tester it's all automatic and I do not have the option of raising the limit.