RCD a pain!

Bruthal

Anyway a megger is next, Switch off the RCD and the MCB for that circuit and test L to E and N to E with all appiances plugged out on the curcuit. If its clear then try same test with appliances plugged in.

M cebee

robbie7730 wrote: »

Anyway a megger is next, Switch off the RCD and the MCB for that circuit and test L to E and N to E with all appiances plugged out on the curcuit. If its clear then try same test with appliances plugged in.

250v between L-E and N-E

L+N bridged

if you're testing with appliances connected

Bruthal

M cebee wrote: »

250v between L-E and N-E

L+N bridged

if you're testing with appliances connected

Yes may as well bridge L-N anyway for the whole test. Id use the 1000v for the appliances plugged out test.

M cebee

sparkfireman wrote: »

Similiar off/on topic question.... Got a phone call just this minute and my head isnt right after an all nite house fire! :O

Jus outta bed...

But my mates immersion element keeps tripping RCD on BATH only...
His ma called an "electrician" friend of hers... who bypassed the RCD and immersion works fine on bath sink... etc....

How is this?? Is the whole tank live?

Cant think...

Someone answer

the immersion will heat partially

the main bond and cpc etc. will take the fault current

Bruthal

M cebee wrote: »

the immersion will heat partially

the main bond and cpc will take the fault current

Well depends on the fault, if the immersion element heating conductor is not broke it will still heat fully usually. But just as often it will be broke and only partially heat, i seen the outer copper split and the element part broke completely and the only circuit path was into the water and it still heated, partially.

M cebee

ya you're right it can be either scenario

Bruthal

M cebee wrote: »

ya you're right it can be either scenario

Bypassing the RCD is a bit nuts though is`t it.

M cebee

it's on a par with registered guys 'selling' certs in my book

Bruthal

M cebee wrote: »

it's on a par with registered guys 'selling' certs in my book

Are they selling them without doing the tests themselves?

SparKing

Well I'm not in favour of selling certs, but if the wiring is installed properly and the job is tested before certifying it then it's not unsafe, is it? So hardly in the same category as bypassing RCDs.
The Ecssa/Reci charge €300 or so to cert I believe, that is a big incentive to buy certs from contractors if you're wiring a house for a nixer.
At this stage I assume the OP has found the problem, what was up?

M cebee

ya right-:mad:

i don't mind being undercut by guys on the dole buying their certs off other contractors

and the sparkie doing the testing is going to enforce any neccessary remedial work-not likely!!

Bruthal

M cebee wrote: »

ya right-:mad:

i don't mind being undercut by guys on the dole buying their certs off other contractors

and the sparkie doing the testing is going to enforce any neccessary remedial work-not likely!!

Well it depends how its done, if a sparks rewires a house and then gets a contractor in who he knows well and they go through every test properly before he certify`s it, i dont see a big problem with that. Whats the difference between that and a contractor employing fellas to rewire some houses. Its not the same as a fella rewiring a house and a fella just sells him a cert without looking at the job.

Certs are only an indicator, not proof a job is done properly, and as a way of knowing who is responsible. If a shower was wired in 10 square but has connectors inside a partition wall, that would hardly be well within regs but would easily pass any tests.

Lots of sparks are on the dole, so should they not do any electrical job at all now? Lots of contractors dont enforce remedial work even on their own jobs or at least they do the quickest thing to get out of it. All the apartments and houses that went up in the big property boom had all sorts of rushed jobs done on them, i found one or two problems in my own house which im sure was certified by the contractor who did it.

If other contractors `sell`their certs without properly looking at and fully testing the job, then its them that are irresponsible more so than the sparks that bought the cert off them. Which was your point in the first place, but if the sparks supplying the cert does`t enforce any remedial work needed then he probably would`t on his own jobs which he has employees on. But just purely selling certs without looking at the job would be mad alright, like i asked before, is this done?

Bruthal

SparKing wrote: »

Well I'm not in favour of selling certs, but if the wiring is installed properly and the job is tested before certifying it then it's not unsafe, is it? So hardly in the same category as bypassing RCDs.
The Ecssa/Reci charge €300 or so to cert I believe, that is a big incentive to buy certs from contractors if you're wiring a house for a nixer.
At this stage I assume the OP has found the problem, what was up?

Well you have to differentiate between buying certs maybe, and getting a contractor to fully test the installation and certify on your behalf.
€300 may be a lot to get reci out to do a cert, but to get a major discount on that then the contractor would have to sell the cert without testing probably, because if he was to go in and fully test the job properly, how much would he charge to do the tests properly and certify. Would it be a lot less than the €300? Maybe it would.

M cebee

robbie7730 wrote: »

Well it depends how its done, if a sparks rewires a house and then gets a contractor in who he knows well and they go through every test properly before he certify`s it, i dont see a big problem with that. Whats the difference between that and a contractor employing fellas to rewire some houses. Its not the same as a fella rewiring a house and a fella just sells him a cert without looking at the job.

Certs are only an indicator, not proof a job is done properly, and as a way of knowing who is responsible. If a shower was wired in 10 square but has connectors inside a partition wall, that would hardly be well within regs but would easily pass any tests.

Lots of sparks are on the dole, so should they not do any electrical job at all now? Lots of contractors dont enforce remedial work even on their own jobs or at least they do the quickest thing to get out of it. All the apartments and houses that went up in the big property boom had all sorts of rushed jobs done on them, i found one or two problems in my own house which im sure was certified by the contractor who did it.

If other contractors `sell`their certs without properly looking at and fully testing the job, then its them that are irresponsible more so than the sparks that bought the cert off them. Which was your point in the first place, but if the sparks supplying the cert does`t enforce any remedial work needed then he probably would`t on his own jobs which he has employees on. But just purely selling certs without looking at the job would be mad alright, like i asked before, is this done?

i'm not concerned about the testing side of it-only the selling of the cert

to non-registered guys drawing the dole and working for 'cash only' that i have to compete against

-it's not a level playing field


i couldn't care less whether they get their houses tested or not:pac:

Bruthal

M cebee wrote: »

i'm not concerned about the testing side of it-only the selling of the cert

to non-registered guys drawing the dole and working for 'cash only' that i have to compete against

-it's not a level playing field


i couldn't care less whether they get their houses tested or not:pac:

True but very little in life is a level playing field, at some stage we could be the fellas on the other side of the inbalance.

Bruthal

Just as a matter of interest RCD problems such as this one are often caused my neutral earth shorts in the circuit somewhere. When there is a neutral earth short or fault after the RCD it can increase the live to earth fault current required to trip the RCD as now some of the earth fault current will end up going from the earth bar to the neutral earth short and back through the RCD. So if 10ma diverted this way it would take 40ma`s to trip the RCD L-E, as in it can increase the trip level to well over the 30ma live to earth current which is the type of current flow when a person contacts between live and earth which causes serious dangers.

Usually when there is a neutral earth short the RCD will trip when appliances are plugged into the affected circuit, and even sometimes when appliances used on other circuits especially heavy loads such as showers. But if nothing is being used it usually wont trip.

M cebee

the 30mA is providing protection against 'direct contact'

the n-e fault won't affect tripping normally on a path through the person to ground anyhow

does it affect it at all on a path back through exposed metalwork or pipework ?

Bruthal

M cebee wrote: »

the 30mA is providing protection against 'direct contact'

the n-e fault won't affect tripping normally on a path through the person to ground

only on a path back through exposed metalwork such as class1 applainces or pipework would it come into play

That may be, but its likely that fatal or dangerous shocks in the home will involve earthed metal work, as a person in dry conditions in the home could touch a 230v point and receive no shock at all if only in contact with the floor, its a certainty that if you contact 230v with shoes on and its dry there will be no perceivable shock unless your in contact with earthed metal. Some will believe that, some might not, but its certain.

Just about any shock we receive involves 2 points of contact besides the feet on the ground.

The other very dangerous one is working in wet conditions using 230v equipment where 110v should be used. But in the home its usually dry and the contact to the actual ground is minimal.

Bruthal

M cebee wrote: »

the 30mA is providing protection against 'direct contact'

the n-e fault won't affect tripping normally on a path through the person to ground anyhow

does it affect it at all on a path back through exposed metalwork or pipework ?

Its actually written somewhere in the regs about the neutral-earth short after the RCD affecting its operation, your certainly right about shocks to earth as in the ground,

When its back through pipework that is earthed to the earth bar it will have some affect, and any earthed metalwork especially when the only path back is to the earth bar rather than a pipe that goes into the ground as well. I would say myself the affect on the RCD is very small, but it is there alright.

But to say the 30ma RCD is providing protection against direct contact only is not entirely right, it will provide protection against any current which does not return on the neutral, so if you have a pipe in one hand and contact a live connection the RCD will trip immediately instead of leaving you exposed to live 230v. If you stand in the middle of the floor and contact 230v the RCD will not trip unless you have a very good contact with the earth.

I would`t recommend this obviously but i`ve tried it all, not all intentionally at times.

Its the reason in a TN system that everything must be cross bonded, so if the earthing becomes live then at least if its all at the same potential it reduces the chance of fatal shocks.

M cebee

i may not have thought the n-e fault situation through:)

anyhow on socket circuits the 30ma rcd is for personal protection-that is it's purpose

Bruthal

M cebee wrote: »

i may not have thought the n-e fault situation through:)

anyhow on socket circuits the 30ma rcd is for personal protection-that is it's purpose

Yes thats its entire design purpose, although it has some very good side effects like when faults develop in elements etc and they do reduce fire risk as you mentioned yourself a while back, one of best inventions in electrical i think.

Bruthal

We often hear that electricity takes the easiest path, but that statement is not really right, it usually takes every path possible, if it only took the easiest path then when you turn on a cooker the lights would go off, so current flowing back to the MCB board earth bar has the neutralising conductor to take back to the transformer, but it also has the path along the earth wire to where its touching the neutral in a fault, and back to the neutral that way which is back through the RCD, this route will only divert a tiny current compared to the easy route back, but some small amount will take it just the same,

The same if a shower is now turned on (or any device but shower is a high load), its neutral path back is to its neutral bar, but another route when there is a neutral earth short in the sockets is from the main neutral bar through the socket RCD onto the sockets neutral bar and down to the neutral earth short and back to the earth bar then onto the neutralising point, this is how a shower can trip the sockets RCD which we seen in another thread, again a tiny percentage of the showers current would go this way and in many cases not enough to trip the sockets RCD, but 30ma out of 35 amps is less than 0.1% so it can happen and does. When a house is neutralised this reduces the chance of this happening as the main neutral bar and earth bar are linked with very low impedence so the diverted current percentage is much smaller.

dingding

robbie7730 wrote: »

We often hear that electricity takes the easiest path, but that statement is not really right, it usually takes every path possible, if it only took the easiest path then when you turn on a cooker the lights would go off, so current flowing back to the MCB board earth bar has the neutralising conductor to take back to the transformer, but it also has the path along the earth wire to where its touching the neutral in a fault, and back to the neutral that way which is back through the RCD, this route will only divert a tiny current compared to the easy route back, but some small amount will take it just the same,

The same if a shower is now turned on (or any device but shower is a high load), its neutral path back is to its neutral bar, but another route when there is a neutral earth short in the sockets is from the main neutral bar through the socket RCD onto the sockets neutral bar and down to the neutral earth short and back to the earth bar then onto the neutralising point, this is how a shower can trip the sockets RCD which we seen in another thread, again a tiny percentage of the showers current would go this way and in many cases not enough to trip the sockets RCD, but 30ma out of 35 amps is less than 0.1% so it can happen and does. When a house is neutralised this reduces the chance of this happening as the main neutral bar and earth bar are linked with very low impedence so the diverted current percentage is much smaller.

Correct, they are essentially Resistors in parallel with some high resistance / impedance in the circuit.