Under sink water heater Rcd?

desoc32

Well this is my first time posting a question and things seem to be a bit quiet here . Anyway i'm trying to find out what is causing the rcd to trip in a kitchen of a small restaurant. They have two 2kw under sink water heaters on the same circuit in staff and customer toilets. The previous sparks disconnected them so i have the task of getting them going again. I belled both heaters out and found that resistance was good on both,the earth was clean and they both heat up grand but once in a while the rcd trips. Is it still possible that one or both of these is at fault due to a slightly split element or something? These are approx 8 years old too and would be on 24hrs a day. Thanks

M cebee

if the IR readings are good, they wont trip an rcd

- unless there's a fault on the final circuit itself

DublinDilbert

When you say you belled them, did you just do a continuity test or megger them?

They must of been disconnected for a reason. If they are wired back to the board you could place them on thier own rcbo's, that would tell you quick enough.

M cebee

when you say you belled them out-are you using a multimeter?
You'll need a megger.

Is there a lot of appliances on the rcd?

desoc32

Continuity test with my trusty fluke multimeter. I don't have any test equipment at the mo. I had run in a new supply from the board to the heaters as the old supply was disconnected somewhere by the last electrician. ( I'm the third electrician at this now!) I should also of mentioned that there is a double socket before the heaters which is where i fed into and made safe the old feed. This socket powers a microwave which for the last while was fed from an extension lead from another rcd'd circuit while it's own socket was off. Now i'd imagine the odd blender etc could be plugged into this socket too. I will put in an rcbo asap and see what happens. If you think meggering might help i'll borrow one from a mate.
Had similar prob now that i think of it with an immersion element which was tripping rcd. Couldn't find the fault with power and resistance was good on element. Decided to change out the element anyway and was a slight split upon close inspection. New element worked grand

M cebee

i would try to megger them and the final circuit if necessary before bothering with rcbo's

-you should be able to check everything in one go at the DB if you can borrow a tester

there's no diversity afaik on thermostatic water heating so you've 4kw +a 13amp socket if they're all on a 2.5 radial?

meercat

if you ran in 2 circuits for the undersink heaters then i would put them on 2 rcbo devices
is it possible that the original rcd is tripping on overload
the 2 waterheaters together will draw 20-25amps
are there any hand dryers etc on the rcd

i would stick the clip on meter on the rcd to test the load

M cebee

meercat wrote: »

if you ran in 2 circuits for the undersink heaters then i would put them on 2 rcbo devices
is it possible that the original rcd is tripping on overload
the 2 waterheaters together will draw 20-25amps
are there any hand dryers etc on the rcd

i would stick the clip on meter on the rcd to test the load

rcd doesn't trip on overload? do you mean mcb?

desoc32

Ok they just tripped again :eek: so i'm gonna go there Monday and pull in a second cable for one of the heaters. Will also try borrow a megger just to see. So that's two new supplies out and i'll have them on seperate rcbos. Belt and braces here! If both heaters and microwave etc are on i suppose it could be using 5000w / 230v so 22amps or more. The hand dryers are on a seperate supply. Diversity definitely doesn't apply here but i think i was allowing myself some anyway as apparently they worked fine for years on old 2.5 supply. Will post back Monday.
Thanks M Cebee and Meercat!

desoc32

M cebee wrote: »

rcd doesn't trip on overload? do you mean mcb?

I was thinking that the mcb would be the one to go if overloaded at 20+amps or live fault etc but it's the rcd that's tripping which makes it more of an imbalance or leakage between live and neutral. Anyway best to have them on their own rcbo's and go from there

meercat

M cebee wrote: »

rcd doesn't trip on overload? do you mean mcb?

i always assumed that once the load exceeded the rating of the rcd,it tripped
remember having a 40amp rcd on a single row board that kept tripping intermittently
replaced it with 63amp one and resolved the problem

meercat

desoc32 wrote: »

I was thinking that the mcb would be the one to go if overloaded at 20+amps or live fault etc but it's the rcd that's tripping which makes it more of an imbalance or leakage between live and neutral. Anyway best to have them on their own rcbo's and go from there

the mcb itself might not be overloaded
the combined load of all the mcbs(water heating/hand dryers/pumps/kitchen equipment)may..... imho
worth checking the load anyway while your at it

M cebee

meercat wrote: »

i always assumed that once the load exceeded the rating of the rcd,it tripped
remember having a 40amp rcd on a single row board that kept tripping intermittently
replaced it with 63amp one and resolved the problem

no ,the 40 and 63amp is just the current rating

meercat

M cebee wrote: »

no ,the 40 and 63amp is just the current rating

learning all the time;)

M cebee

desoc32 wrote: »

Ok they just tripped again :eek: so i'm gonna go there Monday and pull in a second cable for one of the heaters. Will also try borrow a megger just to see. So that's two new supplies out and i'll have them on seperate rcbos. Belt and braces here! If both heaters and microwave etc are on i suppose it could be using 5000w / 230v so 22amps or more. The hand dryers are on a seperate supply. Diversity definitely doesn't apply here but i think i was allowing myself some anyway as apparently they worked fine for years on old 2.5 supply. Will post back Monday.
Thanks M Cebee and Meercat!

check them first before you do any major work

could be that the intermittent tripping is unrelated to the heaters

M cebee

may be a problem somewhere else

accumulated leakage-too many appliances and circuits maybe


you can do the 250V IR test on the outgoing side of the rcd ,might show up a low reading?

Bruthal

meercat wrote: »

learning all the time;)

Indeed, m cebee is correct, an rcd wont trip on overload, unless any slight leakage is also increasing with the increased current. The rating is just what they can continuously carry.

M cebee

meercat wrote: »

learning all the time;)

Same as