New R.C.D.s and TT Earthed Installations.

The test box appears again.......

https://www.youtube.com/watch?v=9qX89cPGgp4

But surely Joe the R.C.D. does not limit any shock current through a human to 30mA or less, it is the body resistance that does that. The R.C.D. just limits the shock exposure time not the current magnitude.

Z.

Interesting.

I noticed their test rig seemed to have the d.c. in a galvanically separated circuit - using a spare pole on the 3ph RCCB or the grey wire on the earth leakage trip. Note sure if that makes any significant difference to having it truly injected into the a.c. circuit.

Since to see some actual figures - even just 50mA d.c. can completely disable a 30mA RCD as far as additional protection is concerned.

  - Andy.

You can do similar experiments with single-phase 2-pole RCD, using a 9 V battery and variable resistor plus fixed resistor (or separated, SELV type, variable power supply and fixed resistor) feeding through the neutral. (Do be careful to design your experimental equipment and test arrangement so you are not exposed to contact with the neutral through ... sorry for stating the obvious but you never know who will be reading this.)

Interestingly enough, generally you see the effects at lower DC current flowing one direction through the RCD to the other direction!

So, are people on TT earthed camping sites or caravan sites' supplies who may plug in a modest electric vehicle charger at greater danger nowadays?

Z.

Zoomup said:

I was wondering if we need to notify all of our customers with TT earthed installations of the need to remove any AC type R.C.D.s and replace them with the newer type A, B or F?

Was this any different to telling them their old VOELCB was no good and they needed to be swapped out for RCDs in the first place (or as some sparks did, try and make TN-S by connecting to the supply cable metallic sheath/armour)?

Worth also considering you might need to tell customers you don't know how effective their older BS 4293 or BS 7288:1990 RCDs are in any case, regardless of DC components, because they didn't undergo the same EMC testing that's now included in the product standards, so they just might not operate when needed?

I guess action as advised by whichever guidance on "coding" you subscribe to?

I still come across the good quality old Voltage operated earth leakage circuit breakers that still work perfectly if the earth wire or rod hasn't rotted away. The Chilton and Crabtree units were made to a very high standard. Some date back to the 1960s.

Some TT sites have dozens of pitch hook ups, the upgrading will cost thousands of pounds and may put the site owners out of business.

Please provide any proven examples where an E.M.C. problem  has prevented an old non electronic R.C.D. from working correctly and causing a hazard.

Z.

Zoomup said:

Please provide any proven examples where an E.M.C. problem  has prevented an old non electronic R.C.D. from working correctly and causing a hazard.

The qualification doesn't work that way ... it works the other way, in terms of placing products on the market that are certified by the manufacturer according to the legislation.

At present, there is no proof one way ... or the other, regarding the "failure" of RCDs under given circumstances (although there is quite a bit of anecdotal evidence of unwanted tripping that is, on the balance of probabilities, caused by "EMC issues").

However, there is a complete absence of evidence that the older products meet the same requirements as newer products ...

I can provide impirical evidence that a lot of older devices still operated reliably. In fact being so large, mechanical and clunky they are certain not to be affect by E.M.C. concerns. I am sure that others can provide evidence of older devices still being fully operational as well.

Edit. Add.....this is a good booklet that explains the operation of the old earth leakage circuit breakers and show the construction of them. It is historical but well worth a read.

www.ebay.co.uk/.../354069837068

Z.

Zoomup said:

I can provide impirical evidence that a lot of older devices still operated reliably.

I'm not saying problems are "guaranteed", but more importantly, safe operation of devices as we know it today is not proven by undergoing the same type testing ... and that's all we do know for sure.

Zoomup said:

In fact being so large, mechanical and clunky they are certain not to be affect by E.M.C. concerns.

Including the effect of harmonics and DC currents (EMC is conducted as well as radiated)?

Zoomup said:

Edit. Add.....this is a good booklet that explains the operation of the old earth leakage circuit breakers and show the construction of them. It is historical but well worth a read.

I like that sort of thing.

VOELCBs in there too? These were another thing entirely, and phased out due to nuisance operation.

Yes, I know about the problems with Voltage Operated Earth Leakage Circuit Breakers. These days with plastic mains water pipes the problem may not exist of fault currents in one house tripping the unit next door.

Z.