odd RCD problems

[nashton]

I have recently had problems with 3 different RCDs but the problem with each was similar. I was called out to sort trip trouble on an RCD (30mA) in a house, client claming that a chainsaw (class 2) kept triping RCD, however no fault was found. Also the RCD pased all normal tests (trip times and ramp tests). However on changing RCD for a new one the problem stopped, and have had this problem two other times. Only common link seems to be age of RCD and items with a PCB causing the problem. Could anyone make a sugestion please.

 

[topquark]

Would an induced current in the cpc affect the RCD which operates on imbalance of the P-N apart from the MEM ones which have the earth reference wire to detect nuetral loss and DC spikes?

No, one that operates from the balance of L/N would not be affected by that.

 

[topquark]

No, one that operates from the balance of L/N would not be affected by that.

Hmm, not unless that is in turn inducing a current in the L or N (in the device itself) ... but that would be a poorly designed device (but could get through testing I guess).

 

[truckster]

Have a read through this pages 32 on RCD Handbook

 

[topquark]

May we assume that the chainsaw is mains voltage and not 110V (via a transformer)?

Think I'm leaning towards the capacitor theory atm. Not sure how you'd prove it easily though.

 

[topquark]

Section 9 makes for an interesting read. The Table 4 on page 39 lists the capacitance to earth values, but that's for Class I equipment only.

 

[topquark]

It does make reference to transient overvoltages by inductive loads causing nuisance tripping as well (like florrys, similarly affecting smoke alarms, when they used to be placed on the same circuit).

 

[truckster]

But it does seem to support your capacitance theory as the items mentioned are chainssaw (motor) and flourescent light (pf correction, start up current) Bit out of my league here

 

[topquark]

Wasn't my original suggestion, it was nashton's http://www.electriciansforums.net/e...orum/35191-odd-rcd-problems-2.html#post295368

Looks like the most likely candidate though.

 

[Electro-tech]

Hi guys, Just to say that my problem with the RCBO is sorted.Replaced with another new one.All okay! They are contactum, not my choice but the Designer.Obvious a Faulty one.?

 

[topquark]

Hi guys, Just to say that my problem with the RCBO is sorted.Replaced with another new one.All okay! They are contactum, not my choice but the Designer.Obvious a Faulty one.?

Good, let's hope nashton comes back with some equally good news

 

[MarkieSparkie]

Nashton what is the supply earthing arrangement?

 

[nashton]

on a TN-C-S system for each of the three different problems ive had. Each time fitting a new RCD has stopped the problem. Does anyone know if with age an RCD becomes sensitive to transient voltages or electrical parts (eg a capaciter)

 

[topquark]

on a TN-C-S system for each of the three different problems ive had. Each time fitting a new RCD has stopped the problem. Does anyone know if with age an RCD becomes sensitive to transient voltages or electrical parts (eg a capaciter)

They utilise magnetic field properties; but there is also a manual part to the RCD that does require periodic use to ensure it doesn't seize (hence the test it every six months requirement with most). If you've noticed the first time you test an RCD that hasn't been used for a while it may have a large response time to the first few trips.

 

[Electro-tech]

Just being Bitchy, "hence the test it every six months requirement with most" as above post. BrB 514.12.2 page 94 ... RCD's Test Quarterly

 

[topquark]

Just being Bitchy, "hence the test it every six months requirement with most" as above post. BrB 514.12.2 page 94 ... RCD's Test Quarterly

Most manufacturers say quarterly as well, so you're allowed to be