>50v Preventing RCD Trip Timing.

[paulh]

Hey Paul H - you're a barrel of laughs aint yah?

It's always good to have a light hearted appoach to a potentially dangerous situation Sorry I will try to cheer up

Bah humbug;\

 

[SPECIAL LOCATION]

Hi SL, Can see what you're getting at - but I'm with Martyn on this.

Applying a few figures to this. Assuming L-L and N- N are 1 ohm. Cross connect and the resistance at any part of the ring should be around 0.5 ohm. If there was a load at the point of measurement of say 200 ohms (just over 1A) then this 200 ohms would be seen to be in parallel with 0.5 ohms - so the resistance would be 0.4987 ohms - a difference of around 1.3 milli ohm. This is too small a value to make any meaniful deductions of how the circuit is wired.

Indeed!

On an electrically intact circuit.. BUT this circuit was at fault!

So either some of the information provided on the earlier posts was incorrect or partial omitted facts...

because if all the readings were OK the RCD would have tripped OK with no potential rise for 50v Touch voltage?

Jim G post#1, some part of this info must be inaccurate!

Issue is with the kitchen ring! R1/Rn & R2 all look good. R1+R2 appears ok. Insulation >200

Jim G post#13, so if Ra 47... for 50v touch voltage. need another 1667-47 = 1620ohms somewhere in the path.. Live through earth! IMHO?

The Ra is 47ohms

Steptoes observation post #14, is a key point?

I fail to understand how your ring can be giving satisfactory results but failing to maintain good earth integrity to allow the RCD to operate.?

Jim G gets to the root of the problem post #18:-

an unswitched fused spur! It was in a mess.The damn thing was corroded almost to pieces. .............. I removed the spur, cleaned-up the cables and simply choc-blocked them together for testing. All is now working ok. Refitted a new spur

I am assuming that these corroded joints that were cleaned and re-terminated were introducing high resistance into some part of the ring circuit..

Which would have shown up on the continuity tests?

i.e. something was far greater than "say 1ohm" per leg to introduce the RCD problem.

when the RCD was proved to be OK?

and a break down in resistance such as would be identified with an insulation resistance test would only create a parallel path to increase the RCD operating speed, not increase touch voltage?

Unless of course I have completely miss read a load of the posts? :| :OBlushing

In which case I will get back in me hutch and eat my cabbage! :|

The main thing is Jim G sussed his problem.

and has learnt not to take stuff for granted even when wiring looks quite newish! post #27

I made the mother of errors and taken things for granted, bearing in mind this install looked only around 3yrs old..... Lesson learned (again)

oh the beauty of hindsight! :^OGuiness Drink

 

[JimG]

I really appreciate all you folks' interaction. This has to be the best forum I've certainly participated in/on.

.... Until the next one :: Cheers all.

JimG.

 

[paulh]

:^OGuiness Drink

See I am a barrel of laughs honest.

 

[Mr Smith]

i will admit .

paulh sometimes makes humerous posts.

mr. smith .

 

[kme]

Stu,

I know what you`re getting at; but:

no offence taken. I didn't want to do an insulation test until I cleared the touch-volt issue

doesn`t appear to mesh with:

R1/Rn & R2 all look good. R1+R2 appears ok. Insulation >200, BUT upon testing the the RCD, my Diolog tester indicates a >50v present

Or is it me?

If the FCU is a spur from the ring, ring continuity will not show it, I think???

I agree with your point of the insul test, however it would detect an unswitched FCU with a load on it...... SO you know to look for something?

Or do i need more carrot pieces from the hamster cage?

 

[SPECIAL LOCATION]

..................If the FCU is a spur from the ring, ring continuity will not show it, I think???

I agree with your point of the insul test, however it would detect an unswitched FCU with a load on it...... SO you know to look for something?

Or do i need more carrot pieces from the hamster cage?

I had assumed the FCU was actually part of the ring..

so making dodgy joints around the leg(s) of the ring..

to many assumptions now... and a couple of missing key facts I think?

but as Jim G sorted it.. I will leave it now

you bring the carrot... I'll get the cabbage..

I guess steptoes may have some bits from Hercules nosebag..Blushing

and we can make a nice Bubble & Squeak for tea tomorrow! :^O :^O:^O

Guiness DrinkGuiness Drink