Melted RCD!!!

[SSE]

My mate asked me to look at his board as a funny smell was coming off it. Looked inside & the neutral going into the RCD was melted & so was the switch. It's a split load dual RCD board. The RCD switches are both rated 64A 30mA. My first thought was that it could have just been a loose neutral but then my second though was maybe the switch wasn't the correct rating. On othis side that the RCD protects he has two rings: one is the downstairs sockets & the other is the kitchen sockets, a 40A shower & a lighting circuit. I know these obviously ain't gonna be drawing their full loads at once but is it still too much?

 

[jaydee81]

63 amp rcd is fine definately sounds like loose connection to me

 

[Marvo]

Most likely a poor termination of wiring into the screw clamp of the RCD. I'm sure you'd have noticed most of the other usual suspects such as condensation, insects, debris ingress from drilling above etc. Some pics may confirm if you can upload a couple.

 

[loop3]

Could well be an over load. At one moment in time at lot of loads could have been running simultaneously. It wouldn't take long to over heat the conductors. then the damage just gets worse.

 

[Sintra]

Loose neutral is the normal cause of what you describe.

 

[Johnny-G]

And it's always the neutral that's loose, I'm waiting for the definitive reason why it's always the neutral

 

[DNS1]

Check the resistance between the neutral bar for that RCD and the incomer. Would expect that to show a high reading, pointing to a loose terminal or a faulty RCD.

 

[Sintra]

And it's always the neutral that's loose, I'm waiting for the definitive reason why it's always the neutral

it was in the OP that the neutral was melted.

 

[Johnny-G]

it was in the OP that the neutral was melted.

Oh I know, I meant it's always burnt out neutrals in general.

 

[Sintra]

Lol they must be the ones that most people forget to tighten.

 

[robsparky1975]

Has all the signs of loose neutral and arcing over a long period of time,seen one recently,80A 30ma main switch,neutral wriggled out easily,so dont expect it was to correct torque,when i had recent assessment the inpsector checked my main switch terminations with his torque driver,spot on,and i dont have one,yet anyway but will get a set as quite handy.

 

[DNS1]

when i had recent assessment the inpsector checked my main switch terminations with his torque driver.

Blimey, didn't know they did that! It's another thing for the shopping list...

 

[snowhead]

And it's always the neutral that's loose, I'm waiting for the definitive reason why it's always the neutral

I have the answer to that one.

It's the same as the Buttered side of toast / bread/ etc, landing on the floor more than the non buttered,, it doesn't.

You remember a neutral being loose, you don't remember the the Live being loose, or even the Earth, on average the same number of times.

 

[telectrix]

seems to be a mindset problem with some sparks. tighten the L dog tight, coz it's the important one, but the N is just a return.

 

[SSE]

Sorry guys have no pictures as I just dumped it. I just replaced it like for like. I'll maybe upgrade it to the next size up though just to be sure...thanks for your help.

 

[Engineer54]

Sorry guys have no pictures as I just dumped it. I just replaced it like for like. I'll maybe upgrade it to the next size up though just to be sure...thanks for your help.

Haha, ...You'll be lucky to see anywhere near 63A for the whole installation, let alone on half an installation!!!

 

[Marvo]

The neutral is more prone to burned terminations than the live because the load on the neutral is higher. Non-linear loads such as fluorescent lighting and switch mode power supplies found in computers and other electronic devices cause harmonics in the triplen range which are especially likely to cause high currents or even overloading of the neutral. The effects of harmonics are usually more profound further up the distribution network but they can be an issue at the consumer end as well.

All that aside, as E54 says, I doubt very much that overload was the issue. I'd still bet on a poor termination causing the overheating.

 

[Jimmy Boy]

What size the tails from the DNO 16's or 25's ?
J

 

[silver surfer]

The neutral is more prone to burned terminations than the live because the load on the neutral is higher. Non-linear loads such as fluorescent lighting and switch mode power supplies found in computers and other electronic devices cause harmonics in the triplen range which are especially likely to cause high currents or even overloading of the neutral. The effects of harmonics are usually more profound further up the distribution network but they can be an issue at the consumer end as well.

All that aside, as E54 says, I doubt very much that overload was the issue. I'd still bet on a poor termination causing the overheating.

I think it's a domestic single phase installation so the neutral current would be the same.

 

[Elmer BeFuddled]

The neutral is more prone to burned terminations than the live because the load on the neutral is higher. Non-linear loads such as fluorescent lighting and switch mode power supplies found in computers and other electronic devices cause harmonics in the triplen range which are especially likely to cause high currents or even overloading of the neutral. The effects of harmonics are usually more profound further up the distribution network but they can be an issue at the consumer end as well.

I concur (well, if I understood!)

I'd still bet on a poor termination causing the overheating.

I'll agree on that as well, never found a (really) loose live or earth, found loads of really loose neutrals.

 

[SSE]

Haha, ...You'll be lucky to see anywhere near 63A for the whole installation, let alone on half an installation!!!

You not think? Maybe my load judegment is a wee bit impaired! lol. I think it's highly possibly, especially when you have a shower running & two rings all on the same side, including the kitchen ring. I may be wrong though!

What size the tails from the DNO 16's or 25's ?
J

25's mate.

I wonder how long it actually would have gone without tripping something.

 

[Engineer54]

You not think? Maybe my load judegment is a wee bit impaired! lol. I think it's highly possibly, especially when you have a shower running & two rings all on the same side, including the kitchen ring. I may be wrong though!

You wouldn't by any chance want to put down any money on it would you?? lol!!!

 

[SSE]

You wouldn't by any chance want to put down any money on it would you?? lol!!!

Mmm you seem very confident so I'll give it a miss. lol.