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I fitted a fan element to an elderly Creda oven last week and whilst testing it the house trip went. The lady reset the trip and I checked out the oven to see where the fault lay? She commented at the time that their trip goes out on a regular basis, even when the oven is’nt in use?
The oven insulation reading at that time was 10 megohms, so well within the acceptable limits overall (I reckon? 😕 ). Fortunately for me the element I fitted was spot on and clear, and so too the other elements and fan motors. But generally the 10 meg reading was from the reostats, thermostats and the wiring harness overall. So no more could be done to improve that reading short of replacing everything.
Since that time, they have used the oven 4 or 5 times with no problems until last night when it was halfway through the cooking process and again the house trip went. The husband gets on the phone to me this morning giving me loads of grief saying the usual crap “It was alright until you touched it!” So I go back out there this morning and check it again….10 megohms still….oven works a treat with all hotplates, grill and oven blasting away….no problem!
He sees it working, I show him the megger reading to prove it is just 10 megohms. I then tell him he needs to contact an electrician to fully check the entire household circuit as I suspect that whilst his oven is cooking away nicely, some other household appliance ( with a slight earth leak) switches on and the combination of two or more (fridge, freezer or boiler maybe?) cause the RCD to trip?
He won’t have any of it, he insists I pay for an electrician to check it out. I tell him of his wifes earlier confession about the trip going on a regular basis. He denies that fact as heresay and irrelavant and we agree to disagree in spite of his bloody oven working beautifully whilst we stand there and argue the toss?
My question to you guys at this point is, what is the minimum acceptable limit for an ovens insulation reading? I am certain I am in the clear on this (at 10 megohms) but if it turns ugly I need a bit a helpful legal advice here perhaps?
Re: RCD tripping house mains?
An entire house test has to be above 1Mohm so this oven is miles inside the limit.
The only thing to check is that the elements don`t go low when they heat and expand but this is extremely unlikely to happen from a reading of 10Mohms.
I do a lot of repairs for our local council after their testers have been and they fail their cookers if the reading is below 1Mohm and this is with them cold.
Hope this helps.
Re: RCD tripping house mains?
bazza500 wrote:Hope this helps.
Indeed, thank you!
But RCD’s don’t play ball @ 1 meg, so what is an acceptable RCD consumer box tolerance I wonder?
Re: RCD tripping house mains?
I cant remember the title but I had cause to check in a book on modern regs (done my time on 14 th edition) nowadays its all talk of disconnection time etc but the point that the author made which stuck with me was “it is sometimes usefull to leave certain circuits off the RCD e.g. cookers to prevent nusance tripping” make of this what you will but I have come across computer circuits freezer circuit etc all seperate from RCD ” TO SAFEGUARD THE APPLIANCE ” so whats the point then? any comments?
Wilf
Re: RCD tripping house mains?
Once an appliance has left the factory IE. it is not new, the “pass” rate for insulation is 0.5M ohm for “new” appliances this is 2M ohm. SO martin, your cooker is “in” by a country mile. Infact many cookers of a certain age are well down approaching or even breaching the safe mark and yet rcd’s are not tripped. My only other thought is tracking within the thermostat which trips out by the spark as the stat opens. Had it on an old Belling the other day.
Better wish them luck with their xmas turkey Martin.Re: RCD tripping house mains?
As said previously minimum insulation resistance is 2 meg, so ok there 😀 .
Could well be a case of cumulative earth leakage as you mentioned Martin.
Haveyou checked the equivalent leakage of the appliance?. So long as the reading is 7mA or less then you’re in the clear :tup:Don’t you just hate those customers who give you that “it was alright til you touched it” crap 😈
HTH
Re: RCD tripping house mains?
Nowt worse than an old cooker for giving you the run around,they’re a pain. I’ve had new elements that test well over 10megs, then after some heats been through ’em down the reading goes! Check the manufacturing date on the mounting plate, some of these elements are not what you would call new stock! Also depends where they have been stored, overnight in yer van at this time of year isn’t ideal, but thats life!
Chris..Re: RCD tripping house mains?
boro wrote:Haveyou checked the equivalent leakage of the appliance?. So long as the reading is 7mA or less then you’re in the clear :tup:
Thanks to all you guys for your comments. It seems my conscience is clear on this job thank goodness. But I will ask boro to explain what he means by the highlighted comment above? Now that I don’t understand I’m afraid, 7mA? Where and how do I check that? 😕
Re: RCD tripping house mains?
Had a job the other day where, when the washing machine was turned on, the house tripped out. No fault on machine itself. The electrician found a fault on the shower which was feeding through the washing machine-socket. This was happening even when the shower was off. 😕
Re: RCD tripping house mains?
He means earth leakage Martin, you need an earth leakage meter to measure it, some PAT testers also have this feature. A clamp meter around the earth will also measure it but not to such accuracies as 7ma.
Re: RCD tripping house mains?
Martin wrote:
But RCD’s don’t play ball @ 1 meg, so what is an acceptable RCD consumer box tolerance I wonder?General purpose RCD to BS 4293
With leakage current flowing equivalent to 50{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} of the rated tripping current, the device should not open.
With a leakage current equal to 100{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} of the rated current then it should trip within 200ms.
There are various other RCD’s to different BS no.s, but in general they should not trip at 50{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d}. The 100{e5d1b7155a01ef1f3b9c9968eaba33524ee81600d00d4be2b4d93ac2e58cec2d} level is time governed. i.e. under 300ms, and 130ms depending on the typeRCD’s have many circuits on them and as Wilf says in general cookers are not usually on the RCD protected side of a “split type consumer unit”. In general only sockets are required to be protected. I say in general as most electricians install a single consumer unit and protect the whole house, in my opinion not a good idea if you have to find the CU in the dark!
Household installation = min of 500000 ohms (0.5 megs) although you should suspect a fault below 2 megs. The same with appliances
Pat tests
Class 1 heating equipment < 3kW 0.3M Ohms
Class 1 All other equipment 1M Ohms (I always double this, 2megs min as Boro says)
Class 2 Equipment 2M Ohms
Class 3 Equipment 250k Ohms10 Megs is far and above what is acceptable.
Martin obviously the guy is getting stick of the misses as well as being a pratt, his misses told you that the RCD often tripped which would says to me that something else other than the cooker may be causing it, especially when you have a good insulation reading (I presume this was taken both when cold and after all elements were allowed to heat up?) If the guy keeps on being a pratt then ask him when the house wiring was tested last? It used to be every 5 years for domestic.
Finally don’t let them get you down and have a good Christmas the same for everyone 😉
Re: RCD tripping house mains?
Now that I don’t understand I’m afraid, 7mA? Where and how do I check that?
Fortuantely for us BSH guys we are provided with a very good Gossen meter that can measure the earth leakage very accurately :tup: .
Unfortunately it sounds asthough your meter doesn’t have this facility 🙁 .
But I still say you’re in the clear with IR reading of 10 meg anyway 😀 .
Re: RCD tripping house mains?
boro wrote:Unfortunately it sounds asthough your meter doesn’t have this facility 🙁
No it doesn’t, I use a Metrohm 500c from Edgecumbe Instruments that measures ohms, megohms and AC voltage. Which is all I need I reckon, and once again, thanks guys for all your information!
:tup:
Re: RCD tripping house mains?
just a thought check the output off appliance and make sure it dosn’t need to be on a 10mm cable with a 40a breaker if its on a 6mm cable then it could be breaking down under heavy load i know the regs say you can have upto 15kw on a 6mm 30a breaker because of the diversity factor but that is just rubbish in my opinion have it all the time.Do a lot of work for a kitchen company as an electrian now and see quite a few things the ones that get on my nerves at the minute is some bosch single ovens with an output of 3.1kw 3.3kw and 3.5kw and bosch say they can go on a 13a plug top! and then you gussed it either the socket or plug decides to melt under the load and you end up havin an argument with the customer trying to advice them and them saying bosch says you can do it like that so you must be wrong! aaarrrghhh customers! why do they bother to call you if they already know more then you??? sorry rant over but yes 0.5 meg is fine for r.c.d and cooker only needs to be on r.c.d if got a socket outlet on it and thats if you think there is a chance of it being used for outside use. merry christmas to all
Re: RCD tripping house mains?
My thoughts on this one is. Becouse it has happend before you turned up Have they had the fuse box replaced. Sounds like it may be a split load consumer unit.
Clue to this take cover off CU and two neutral bars so if everything is ok untill something else where is swithed on. Current returns on wrong neutral trips RCD.Have you all seen the proposals for the new 17th regs? Big changes regarding the use of RCDs
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