Trainee Question RFC circuit ??

[BeatBox]

Hi

new to this site. I am a trainee electrician and have been trying to get some info on ring final circuits. My parents have had there kitchen done, well new worktop and doors all spray painted. They have installed a new larder unit and they are looking to plug in micro/oven/grill in the larder unit which there is a existing plug behind where the kitchen larder unit is.This socket is installed on kitchen/utility ring. It is a 5 bed house. With the following circuits
32amp cooker circuit
32amp downstairs ring
32amp upstairs ring
32amp kitchen/utility ring
6amp lighting upstairs
6amp lighting downstairs
20amp water heater
20amp garage supply.

so the micro/ oven looking to plug this in to kitchen/utility ring. But already on kitchen/utility ring is
Washing machine - 2kw
Tumble drier - 2.2kw
Dishwasher - 2.1kw
Kettle - 3 kw
Toaster - 1.5kw
Cooker hood - 80watt
Utility fan - 30watt

and I am looking to plug in the micro/oven/grill which is rated to 2.3kw overall. Would this be possible. I heard something regarding diversity on ring circuits that appliances will not be on at same time or pulling same current at same time. Is that correct ? The issue with running new cable in is its concrete floor and artex ceiling so would rather keep it on kitchen ring. Just hope this won’t be overloaded ?? Replies/advice will be very grateful

 

[nicebutdim]

Not RCBO, but delay RCDs come in both flavours even if the suppliers are often not terribly open about it.

Let me get this straight as I'm starting to get confused. What I'd originally been thrown by was the highlighted section of the post quoted below, which I'd taken to have confused the designations for two separate characteristics.

If I understand correctly RCBOs are available in types AC, A, B and F. RCDs are also available as type S (time delayed).

Sticking with RCBOs, the overcurrent trip characteristics are B, C or D curve.

Forgive (and correct) me if I've used incorrect terminology, but is the above broadly correct or is there more to the highlighted quote below than I realise?

You could have DC leakage effectivly blinding a type AC RCD resulting in a reduced chance of it operating at it should - but you wouldn't know about it (or rather how much) if you didn't test for it.

By testing for leakage (type and amount) you have the chance of futureproofing the install by changing the breaker type to deal with the expected leakage better. I don't have my books handy but I'm sure general rule was Type D can take more DC leakage than Type C, C can take more than B, B can take more than A and A can take more than an AC.

 

[Lister1987]

Let me get this straight as I'm starting to get confused. What I'd originally been thrown by was the highlighted section of the post quoted below, which I'd taken to have confused the designations for two separate characteristics.

If I understand correctly RCBOs are available in types AC, A, B and F. RCDs are also available as type S (time delayed).

Sticking with RCBOs, the overcurrent trip characteristics are B, C or D curve.

Forgive (and correct) me if I've used incorrect terminology, but is the above broadly correct or is there more to the highlighted quote below than I realise?

As I say NBD, I could be spouting myself to to me it makes sense. Joe public isn't going to know a General Purpose circuit from another type. All they see is s socket.

My point was trying to (and probably epic failing) to get an electrician thinking about how seemingly a normal device (washing machine for example) may cause negative effects on a circuit - DC leakage being the main - based on how much electronically is going on in these things (and white goods in general) and as a result the negative effects (DC Leakage) crippling a device that isn't designed to handle it (AC type RCD v A type RCD).

So what could start out as " please add a few sockets in my new laundry room" (and you might just extend the kitchen ring, which shares an RCD with half the house) will actually turn into 'a whole new circuit on a different type of RCD/RCBO due to the excessively high amounts of DC Leakage caused by the HAL9000 combination of her washing machine, tumble dryer and dishwasher smart tech - or the cumulative DC Leakage of not only the kitchen ring but also whatever other circuits are leaking DC current and blinding the shared RCD because Type AC will only handle so much, of any DC Leakage.

You'd check for DC Leakage if you were called out to nuisance tripping, so why not check for existing leakage before doing any work/alterations?

To me it makes sense (part of the selection and erection process) and just seems like something good to help better your understanding of the install you're working on.

I'll shut up now as o Dr to have derailed the thread a bit ?

 

[nicebutdim]

I get what you're driving at and similar thoughts have ran through my own mind. A good part of the reason for my being here is to reconcile such questions in my own mind and try to understand whether or not there is any foundation to them.

I picked up on that particular point because one of us was going astray - which of us was of little consequence, but it seemed like a good idea to straighten out the facts.

 

[davesparks]

sure, I get that the list of appliances is "standard" but knowing how much leakage (and type of leakage) would put a spark in a better position to advise the customer.

You could have DC leakage effectivly blinding a type AC RCD resulting in a reduced chance of it operating at it should - but you wouldn't know about it (or rather how much) if you didn't test for it.

By testing for leakage (type and amount) you have the chance of futureproofing the install by changing the breaker type to deal with the expected leakage better. I don't have my books handy but I'm sure general rule was Type D can take more DC leakage than Type C, C can take more than B, B can take more than A and A can take more than an AC.

Am i making sense, hoping it doent sound like i'm talking out my arse, which isnt unsual i grant you.

You still haven't answered what testing you are suggesting?

I don't own test equipment suitable to measure what you are describing here, and I doubt may electricians do.
You'd need something which can record earth leakage over a period of time as all of the appliances are used for their full cycles/normal usage, and probably in combinations of different appliances running at the same time. The tester would need to be capable of measuring both AC and DC leakage for what you are asking.

In short that's likely to be a very expensive tester and an expensive process of testing.
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You'd check for DC Leakage if you were called out to nuisance tripping, so why not check for existing leakage before doing any work/alterations?

To me it makes sense (part of the selection and erection process) and just seems like something good to help better your understanding of the install you're working on.

I wouldnt immediately check for DC leakage if I was called to a nuisance tripping fault, at the moment the leakage clamp meter I have is AC only, I'm sure a lot of other electricians are in the same position.

It doesn't make sense to me as part of selection and erection, without a detailed analysis you will only get a snapshot of the situation at a particular moment in time.

To me it's no different to the people who put a clamp meter on the tails for a few minutes to establish whether there is capacity for extra load or not, it normally needs a load study for at least a week to establish peak and average demand.

 

[Lister1987]

Surely the type of testing is evident? Testing for leakage to earth (AC or/and DC with a clamp meter with suitable resolution) and getting some idea (rather than no idea) or what you are facin (and whether or not a cumulative leakage could give rise to undesirable interference with RCDs that aren't designed to handle DC leakage - The move away from AC type RCDs to type A; I'm lead to believe that is primarily down to cumulative DC leakage from modern day tech and the drive to smart tech and how that DC leakage interferes with the RCD effectiveness.

I'm not saying a 10-20 minute monitoring with a clamp meter attached will give you every piece of info you want, I'm saying it might provide a puzzle piece for an issue that may occur due to a change you make.

I'm not saying I'm right or you're wrong (or vice versa), just putting forward something that to me seems like a good idea as something to check; Not to dissimilar to whacking a clamp meter on the service head, with the fuse removed, to check for diverted neutral currents - Something that until recently I gave zero thought to, bit after discussing it with people, I got it.