Failed RCDs

[sambev]

I'm the Facilities Manager for several schools in the West Mids. Our M & E contractor has just failed 53 RCDs at 4 schools. The schools are only 3 years old. Is this normal?

 

[ianmacd]

Have they not been regularly tested with the test button every 3 months?

Welcome to the forum.

Ian.

 

[sambev]

Thanks Ian

Yes we've had 2 minor and 1 major service annually. The school I'm based at is 7 years old and we've had no failures.

 

[ianmacd]

There should normally be a label near the RCD like the one below suggesting pressing the test button every 3 months to confirm it is working as expected.

Has an RCD test peen performed at these services?

 

[The Godfather]

I'm the Facilities Manager for several schools in the West Mids. Our M & E contractor has just failed 53 RCDs at 4 schools. The schools are only 3 years old. Is this normal?

The Don would like to know, why they have failed them?

Are they failing to trip, or are they exceeding trip times?

And more importantly, where they tested without any circuits connected?

Don

 

[WarrenG]

Sambev, 53 seems an awful lot to me? It is probably better to dig deep and find out exactly why these units have been failed by the contractor?

Are they all the same make? Do you have any testing records for the tests carried out?

There are parameters that the RCD should fall into based on the tripping times of the unit and checks to make sure the fuctionality side of the device (the mechanical side of the unit) switches correctly. It is important that the tests are carried out correctly as they can be sensitive.

I would be interested to hear the reasons why they have failed based on your contractors feedback?

I am based in the West Midlands. Should you wish to discuss the testing records further just PM me.

Warren

 

[batty]

Hello sambev welcome to the forum. That seems strange to have that many failing. I test with a fluke 1652 tester it is away at the moment being repaired as it was failing all Rcd's. It would only trip them out at 5 times test. Just a thought that maybe whoever tested them may have a faulty tester.

Batty

 

[The Godfather]

Schools do have a large number of PC's installed, my view is that the RCD's have been tested with live circuits, not a good practice.

(Even if they were switched off, but not unplugged)

Don & His Boys

 

[green-hornet]

There was a thourough examination carried out by the electrical safety council on rcd,s about two years ago.

They tested a hell of a lot more than you would have in all the schools.

The results of the tests proved that about 80% of failed rcd's on site proved ok in the lab.

Out of all failed units ony 1% proved a positive failure, and was mainly caused by poor maintenance.

To say you have 53 failures would go against all recorded data on rcd tests carried out to date, and would in fact cause a major upset in the electrical industry, similar to an airline going down with no immediate reason.

I would assume the contractor has greatly misinterpreted recorded data, or scheduled maintanance has been neglegted for a number of years.

As a foot note the major cause of rcd failure was put down to contaminated contacts ie dust, simply dislodgement of this dust allowed most failed units to operate propely.

 

[Andy™]

Schools do have a large number of PC's installed, my view is that the RCD's have been tested with live circuits, not a good practice.(Even if they were switched off, but not unplugged)

Don & His Boys

why is it a bad practice though? as mentioned in a thread a few weeks ago, certain things may delay an RCD tripping, but removing item to make it pass doesnt make the installation safe. would you be happy sending your kids to a school where tests have proved an RCD will not trip when computers etc are plugged in, but the sparky unplugged them to get it to pass testing?

 

[green-hornet]

why is it a bad practice though? as mentioned in a thread a few weeks ago, certain things may delay an RCD tripping, but removing item to make it pass doesnt make the installation safe. would you be happy sending your kids to a school where tests have proved an RCD will not trip when computers etc are plugged in, but the sparky unplugged them to get it to pass testing?

Very good point raised there.

The tests on a rcd are very basic, there is another reason why 53 RCD units failed this test.

Electrical contractors often fit as standard 30mA for socket outlets.

I know for safety reasons some education authorities would demand 10mA.

All science labs wouls normally need 10mA protection, but some schools would require all to be 10mA and not 30mA.

May be that the tester is working to the local education authority guidlines and has failed 53 rcd units because they are the wrong type.

 

[bigclive]

I'm the Facilities Manager for several schools in the West Mids. Our M & E contractor has just failed 53 RCDs at 4 schools. The schools are only 3 years old. Is this normal?

That is an unusual number to fail within 3 years. It would be interesting to see why they had failed them.

Possibilities could be:-

Bad batch when the schools were wired.

Bad tester out of spec.

Tester operated by dumpling. (M & E contractor after all!)

Tester told to fail some stuff to generate work.

 

[Andy™]

how many didnt fail?

 

[WarrenG]

Would agree with Doc that testing with live circuits isn't going to help the situation at all, and especially with any pc kit that requires a natural earth leakage. Hence the resaon we unplug for the duration of the test.

If there is equipment plugged into circuits protected by the RCD that has leakages, these will be picked up by the RCD and the test results will show inaccurate readings because the RCD may not trip in the required times due to the excess of leakage current.

Example 20 computers each with a leakage current of 1mA added to the 15mA half test current will be reated over the tripping current of the RCD.

Any equipment with leakage current may be low enough to not trip the RCD in normal use but when added to the test currents show inaccurate results. This would make the RCD look faulty.

Typical equipment with high leakages include electronic equipment with mains input filters, washing machines, fridges, grills, immersions, ovens etc.

 

[m4tty]

sorry to ask but this may be a stupid question if i have misunderstood the above but are you saying that when you press the rcd test button should all mcb's be turned off with no load on?? if you get me cheers

 

[Andy™]

RCD's should be tested as close to RCD as possible, and an isolation from everything else. but in the real world, its easier to plug test kit into a socket

 

[sarni31]

sorry to ask but this may be a stupid question if i have misunderstood the above but are you saying that when you press the rcd test button should all mcb's be turned off with no load on?? if you get me cheers

The T button tests the mechanical operation of rcd only by apply an internal short. So in answer to your question for this test on or off load would make no difference.

Guiness Drink

 

[binky]

Sounds like a second opinion is needed - I would get a different electrician to re-test and confirm/ repudiate results. 3 years is not old for an RCD and should still be working even if not regularly exercised.

 

[Janice]

I notice that the OP has not come back to answer any of the members' queries after their original post - end of thread, methinks.

J.

 

[The Godfather]

We shall see.

Don & His Boys