Ring to radial

[AdieB]

Had a call out to a home where the RCD keeps tripping when lounge ,dinning and bed room sockets mcb is switched on. Fault traced to one of the legs from the consumer unit to 1st socket 0.2Meg ohm at best. cable size is 2.5mm T&E there are 10 double and 4 single sockets on the circuit. Reg 433.1 seems to indicate that providing the floor area is limited to 50 m2 (the area in question is 3/4 the floor area of a medium size house. it would be ok to drop out the damaged leg from the consumer unit and socket fuse down to 20Amp mcb and leave as is. Possible to rewire initial leg and reinstate ring but do I need too?

what do you think?

AdieB

PS dropped leg out of consumer unit marked cable with tape and description of fault. Disconnected from socket and put wago type terminals on he cores. Changed mcb to16A (close's that was on van.)

 

[GMES]

Sorted.
Cheerz dude.

Suits you Sir

 

[VoltzElectrical]

Suits you Sir

Working on the tash but got the salute sorted!

 

[GMES]

oh my god. Exactly what I was going to say. Absolutely ridiculous. Some on here just look for holes and use that to flex their BYB muscles.

Crap. You are obviously out of practice.

Yawn!!!

I think he may be the 1st on mine if things carry on.

 

[Guest125]

Uk It wasn't long ago that you were complaining that members were having a pop at you all the time!!
It cuts both ways. A debate is one thing, baiting another member is another thing.

Point taken. Apologies. My point that in all reality this is not worth a design still stands. I just think he does this for the sake of argument.

 

[Guest125]

Ignore the people around you that may be able to help is short sighted. I don't agree with a few people on here but I would not ignore them. Listening to others is a good thing.

 

[TJ Anderson]

Pure laziness. Besides what happens if the RCD fails?

Replace the faulty leg get it back to how it was before and get paid.

Hang on, that's the customers decision, not yours, I'd have no problem doing either. Give the client the options if they want limited capacity or reinstate the RFC. Also Dilb, I would test RCD in the course of my work. If you think down that track, what if the MCB fails? what if a mouse eats the cable insulation? what if there is a power surge? What if, What if, What if?

 

[tazz]

Point taken. Apologies. My point that in all reality this is not worth a design still stands. I just think he does this for the sake of argument.

You need to expand more, if your going to debate an issue, so people can see your point of view.....Crap, and I disagree don`t say much..

 

[Guest125]

You need to expand more, if your going to debate an issue, so people can see your point of view.....Crap, and I disagree don`t say much..

I know. I am sorry. I bit. There are 3 on here that get my back up but that is my issue not theirs. I am willing to accept I was at fault here. Sorry all!!!

 

[Guest125]

I really think any spark worth their salt would give the client two options:

1) reinstate ring (surface or chased)
2) change to a radial circuit

cable calcs are done. In the head of a guy who has enough experience to make these calls.

 

[7029 dave]

What do I think?

Stop being idle and get on with replacing the faulty leg and reinstate the ring.

Had the fault been at a mid point I may have agreed with making it two radials. No way would I agree to making a single radial and down rating by 62%.

In an nut shell.

 

[VoltzElectrical]

You need to expand more, if you're going to debate an issue, so people can see your point of view.....Crap, and I disagree don`t say much..

Now, now. "debate, but don't insult."

Lol.

 

[HappyHippyDad]

Had a call out to a home where the RCD keeps tripping when lounge ,dinning and bed room sockets mcb is switched on. Fault traced to one of the legs from the consumer unit to 1st socket 0.2Meg ohm at best. cable size is 2.5mm T&E there are 10 double and 4 single sockets on the circuit. Reg 433.1 seems to indicate that providing the floor area is limited to 50 m2 (the area in question is 3/4 the floor area of a medium size house. it would be ok to drop out the damaged leg from the consumer unit and socket fuse down to 20Amp mcb and leave as is. Possible to rewire initial leg and reinstate ring but do I need too?

what do you think?

AdieB

PS dropped leg out of consumer unit marked cable with tape and description of fault. Disconnected from socket and put wago type terminals on he cores. Changed mcb to16A (close's that was on van.)

0.2MΩ isn't anywhere near enough to trip an RCD, it needs to be closer to 0.008MΩ so perhaps some more investigation is required. Could you confirm what the poor IR test results refer to? L-N or N-E? I have to assume N-E, but it would be good to just know for sure as 0.2MΩ does sound like something plugged in or a neon?

It's not impossible for there to be a fault with the actual cable run but it's much more likely that the fault lies with an appliance or at a socket/FCU. Have you made absolutely certain that there are no other connections between the CU and this '1st' socket. Perhaps hidden in a cupboard?

As for changing to a radial, I think that is an option once some more investigation has taken place to find the fault. Also, like the others have said the floor space would have to be <50²m and the Electricians Guide to the Building Regs suggests <40m total run length as well. Also I would want to work out what the max demand is 'likely' to be for this circuit before changing to a 20A radial, this could affect your decision.

But.. it also depends on how 'Possible to rewire initial leg' it is if you do find the fault to be hidden in the fabric of the building? If it's easy then decision made, if not then you may sway towards a radial.

 

[TJ Anderson]

0.2MΩ isn't anywhere near enough to trip an RCD, it needs to be closer to 0.008MΩ so perhaps some more investigation is required. Could you confirm what the poor IR test results refer to? L-N or N-E? I have to assume N-E, but it would be good to just know for sure as 0.2MΩ does sound like something plugged in or a neon?
.

There will be other earth leakage in parallel with this 0.02M/Ohm circuit N-E issue. Also a L-N fault would not trip RCD, it must be L-E or N-E for earth leakage. I would hope he has disconnected all loads.

 

[HappyHippyDad]

There will be other earth leakage in parallel with this 0.02M/Ohm circuit N-E issue. Also a L-N fault would not trip RCD, it must be L-E or N-E for earth leakage. I would hope he has disconnected all loads.

I realise this TJ, but it would just be nice to see it written clearly, much easier to form an opinion then. Also it was 200,000Ω not 20,000Ω, 200,000 is a long way from 8,000 so thats a lot of parallel earth leakage!

 

[Knobhead]

Even if Zs was a bit over for MCB, which it almost certainly won't be, I would have no problem in utilising the 30ma RCD to provide satisfactory earth fault disconnection in this instance. This is not designing new circuits, this is getting someone up and running when they have a problem.

As a temporary measure then yes. NOT as a permanent fix!

As for relying on the RCD, is this the depth the trade has sunk where supplementary protection has changed its role?