Guess the fault

[p11jor]

Had a call out late last night, everytime the shower comes in it's blows the whole house.

The set up of the board is duel rcd. 2 mcb either side.

Cooker/shower on left

Lights/sockets on right



So the power to the shower switch is fine, again this can function fine and send power to the shower, bit as soon as the shower is pressed is wipes both rcds straight out after 2seconds.

I did a insulation resistance test, was getting 0.25megohms.
Removed tge switch and was getting 459megohms. So thought new switch, put new switch on and still wiping the whole board out, but obviously were not getting a dead short as the power to the shower is fine untill pressed.

Quite interesting this one. But such a obvious one which I will always look out for on my future PIRs

 

[pmac10]

p11jor, luckily i'm not let loose near domestic dwellings, but i would guess 250V, the elements would be the next electrical component energised after your switch is pressed and the rcds trip

 

[vernam616]

Okay, Okay, I'll stop commenting now

Haha you seem to know your onions

 

[p11jor]

To be fair vernam I think there's a big divide in electricians.

There are people who have completed 2330, 2382, 2391 and become part p registered due to carrying out work all to regs and can test and certify it ,

Then there are other sparks who have all this but are very switched on and can pick faults out in a instant, there the engineers, there are some very good ones on here that's have helped me massively,

Others on here are really helpful and are good enough to offer some help (right or wrong) and I bet from a installation point of view they are good.

 

[topquark]

Haha you seem to know your onions

I have a basic food hygiene certificate, "I'm just a cook".

Must admit it would be good to ascertain exactly why that causes a trip. I would guess that as the one RCD is shutting down the busbar for that RCD approaches zero and that causes a jump from the Other RCD's busbar to the first (causing another imbalance in that 2nd RCD).

 

[vernam616]

But if thr help is wrong theres a major flaw, someone advises you its ok to do something and it clearly is a ill fated comment, you are then risking your own working practices, i agree there is a lot of people on here who know their stuff, unfortunatley there is also the opposite, i dont mind helping anyone with the knowledge/experiences that i know but i wouldnt say anything unless i was absoutley certain it was correct

 

[p11jor]

That's were the likes of yourself comment in and its great because your helping them aswell as the original post. Ok there may break into a row etc but 9 times out of 10 the correct advice would be posted on
Here from a member who is more in the "kno"!! I can't think of the members I have had good advice from from top of my head but certainly "telextric" if thats how he spells it is very good.

 

[p11jor]

Add topquark to that list too then !!!

 

[GLENNSPARK]

Surely power`s got nowt to do with it ("jumping across") it would be force (pressure) wouldn`t it....: voltage...and as for arcing....isn`t that a EMF caused when an inductive load is suddenly disconnected from its supply...isn`t this based on one of michael faraday`s great discoveries.....

 

[topquark]

Yep, just Voltage, a PD caused between the two (very close) bus bars as the first RCD is cutting the power.

 

[ackbarthestar]

There was no continuity between neutral & earth and untill the shower is switched on from the body of the shower not the iso switch then we are all good and no tripping. But when the shower was activated both rcds and all 4 mcbs blew.

I think you may need to explain this. Two neutral bars are placed together 6mm apart. Unfortunately there is a bloke on the TV with a converted gas mask into a bong... impressive ! (Knocked up)
The obvious fault is a crossed neutral (neutrals in the wrong bars). But this gets more interesting when not only both rcds trip but all 4 mcbs go as well! Did you get a good deal on ebay?
One other suggestion, use a bit of outer sheathing between the bars, don't bother to cut the neutral bars

 

[Rockingit]

Just thinking about this.... the shower load is inductive (mostly), so when the circuit collapses there's a whole load of back EMF happens, disproportional to the original supply load. Now, when it hits the Neutral bar it's then also looking at another magnet (the balance coil inside the RCD) which is (probably) still experiencing it's own collapsing field and associated EMF going the other way (see Flemings Left and Right hand rules)....so...what we have is a whole load of inductive energy looking for a place to hide. Introduce another conductor a bit too close, also connected to a coil (the other RCD) which is energised normally, and it's going to try to join the party. Second RCD then gets inbalanced and trips also.

Just a guess.....think I'm going to retrain as a hairdresser or cook or something.

 

[topquark]

That's a possibility, particularly relevant if the shower/shower circuit doesn't have any fault.

 

[ackbarthestar]

Just thinking about this.... the shower load is inductive (mostly), so when the circuit collapses there's a whole load of back EMF happens, disproportional to the original supply load. Now, when it hits the Neutral bar it's then also looking at another magnet (the balance coil inside the RCD) which is (probably) still experiencing it's own collapsing field and associated EMF going the other way (see Flemings Left and Right hand rules)....so...what we have is a whole load of inductive energy looking for a place to hide. Introduce another conductor a bit too close, also connected to a coil (the other RCD) which is energised normally, and it's going to try to join the party. Second RCD then gets inbalanced and trips also.

Just a guess.....think I'm going to retrain as a hairdresser or cook or something.

Hairdressers couldn't provide that explanation, even for their curling tongs but nevertheless a nice explanation... if it were an inductive load, but I think you will find that it is purely resistive, even though its coiled up, remember all of the conductors (phase neutral and earth are coiled together, like an ext. lead).
The problem still exists why does everything go Pe-tong when the shower switch is pressed?

 

[GLENNSPARK]

Just thinking about this.... the shower load is inductive (mostly), so when the circuit collapses there's a whole load of back EMF happens, disproportional to the original supply load. Now, when it hits the Neutral bar it's then also looking at another magnet (the balance coil inside the RCD) which is (probably) still experiencing it's own collapsing field and associated EMF going the other way (see Flemings Left and Right hand rules)....so...what we have is a whole load of inductive energy looking for a place to hide. Introduce another conductor a bit too close, also connected to a coil (the other RCD) which is energised normally, and it's going to try to join the party. Second RCD then gets inbalanced and trips also.

Just a guess.....think I'm going to retrain as a hairdresser or cook or something.

Heating loads are resistive mate...That is to say both voltage and current can be said to be IN PHASE with each other....

 

[Rockingit]

Heating loads are resistive mate...That is to say both voltage and current can be said to be IN PHASE with each other....

Unless you're an induction heater!! But fair enough, like I said, was only a guess. Right - where's my scisssors??!