Cooker cable/mcb rating
- Thread starter stanna
- Start date
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The 2.5mm² flex is too small for a 32A MCB.
Either exchange the flex for 4mm² (easier) or
Exchange the 32A MCB for a 20A.
What do the Manufacturer's Instructions state?
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Simple answer it needs altering. However as we start to look more carefully then one has to question does it really? 2.5mm thermosetting cable clipped direct is rated 33A however unlikely it is clipped direct. The oven wants 21A and most MCB's ranges jump from 20A to 32A so either one slightly overloads a 20A or you use a 32A which would mean you need 4mm cable.
The Batt cables web site has this PDF which clearly states:-
0.5mm = 3A
0.75mm = 6A
1mm = 10A
1.25mm = 13A
1.5mm = 16A
2.5mm = 25A
4mm = 32A
However the table is for 60 degrees and the cable is rated 80 degrees but the 17th Edition says we should follow manufactures instructions so since Batt Cables are the manufactures if they say Table 4F3A should be used we don't really have an option.
If you can fit a 25A MCB then that would seem simple way out. But what happens then is in 10 years time you come to replace the oven and use an electric hob and you are told the supply is not big enough and the electrician does not know if the MCB was changed due to oven size or because the cables runs through insulation. So it is very important to keep the paperwork raised so it can be changed back at a latter date.
Hi,
I hope nobody minds me jumping on this old post, but I have a similar question.
I wish to replace a gas cooker with an electric one rated at 9.4KW. I'm trying to work out the specs of the cable and MCB I need to purchase.
The manufacturer states that I require 4mm2 cable and 32A MCB (minimum).
A little bit of maths gives me: I = P/V = 9400/230 = 40A
4mm2 cable, enclosed in a conduit, in an insulated wall is rated at 32A.
(http://www.batt.co.uk/upload/files/currentratingstable4d1a_1312875628.pdf)
From my calculations, I should be looking at a 40A MCB and 6mm2 cable. The only thing I can think of is the manufacturer assumes one will not have the oven, grill and for 4x "burners" running at the same time. If they were, the MCB would trip assuming the cable is rated greater than the MCB.
Can anyone advise if I should "upgrade" or use 4mm2 + 32A MCB?
This will be a radial circuit of no more than 2 meters from the cooker to the CU I calculated the VD as 0.57V (0.25%), well below 4%.
(mV/A/m) x Ib x L = (7.13 x (9400/230) x 2)/1000 = 0.57v
% VD = (VD/Source Voltage)x100 = (0.57 / 230)x100 = 0.25 %
Many thanks
W.
P.S. Manufacturers install guide: http://downloads.beko.co.uk/bekoupload/manuals/BDVC563AW.pdf
I hope nobody minds me jumping on this old post, but I have a similar question.
I wish to replace a gas cooker with an electric one rated at 9.4KW. I'm trying to work out the specs of the cable and MCB I need to purchase.
The manufacturer states that I require 4mm2 cable and 32A MCB (minimum).
A little bit of maths gives me: I = P/V = 9400/230 = 40A
4mm2 cable, enclosed in a conduit, in an insulated wall is rated at 32A.
(http://www.batt.co.uk/upload/files/currentratingstable4d1a_1312875628.pdf)
From my calculations, I should be looking at a 40A MCB and 6mm2 cable. The only thing I can think of is the manufacturer assumes one will not have the oven, grill and for 4x "burners" running at the same time. If they were, the MCB would trip assuming the cable is rated greater than the MCB.
Can anyone advise if I should "upgrade" or use 4mm2 + 32A MCB?
This will be a radial circuit of no more than 2 meters from the cooker to the CU I calculated the VD as 0.57V (0.25%), well below 4%.
(mV/A/m) x Ib x L = (7.13 x (9400/230) x 2)/1000 = 0.57v
% VD = (VD/Source Voltage)x100 = (0.57 / 230)x100 = 0.25 %
Many thanks
W.
P.S. Manufacturers install guide: http://downloads.beko.co.uk/bekoupload/manuals/BDVC563AW.pdf
The manufacturer is correct.
Nice maths.. but you forgot about diversity….
HAve a read about it here, and it will make mopre sense.
http://www.tlc-direct.co.uk/Book/6.2.1.htm
Nice maths.. but you forgot about diversity….
HAve a read about it here, and it will make mopre sense.
http://www.tlc-direct.co.uk/Book/6.2.1.htm
If the manufacturer had read that, he might not even have necessarily asked for 4mm² cable (19A, or less, after diversity), although it probably would not be sensible to use anything less than 4mm² for a cooker circuit (and obviously essential with some installation methods).
Given that he is talking about the spec for new cable and a new MCB, it sounds as if the OP is talking about a 'new circuit'. If so, it would obviously be notifiable work - which means that it would almost certainly be cheaper for him to employ a self-certifying electrician than to do it (and pay LABC fees) himself.
Kind Regards, John
Hi Taylortwocities,
Many thanks for your reply.
So diversity makes the assumption that one will not “max out” the circuit and if they do, the design will mean the circuit breakers will trip. With regard to a ring main, with multiple 13 amp sockets, that assumption make perfect sense and of course reduces costs.
With regard to the cooker, the manufacturer has also applied diversity, somewhat greater than the regs suggest, but in essence, the manufacturer is suggesting that one will not run the oven, grill and all four burners at the same time. I would argue this scenario should be catered for. Think Christmas lunch. Or is it a case that the cooker itself cannot handle this?
I notice the manufacture states the fuse should be 32A minimum, so as I am adding a socket, I need to cater for this by increasing the fuse rating.
In the link you provided (BS7671, OSG, Table 1B), when applying diversity for cookers in a domestic installation, diversity is calculate thus: 10A +30% f.l. + 5A (w/ socket).
The manufacturer specifies:
Burners: 1200W, 1700W, 1200W & 1700W (5800W)
Top oven: 1600W
Main oven: 2000W
Connected load: I = P/V = 9400W / 230V = 40.87A
Applying diversity = 10A + 30% x (40.87A – 10A) + 5A = 24.26A
So for arguments sake, let’s say I had the oven on, drawing 2000W, 1x 1700W burner and a 2300W kettle boiling away. The connected load would then be: 8000W/230V = 34A. My MCB has just tripped!
As I have the additional socket, would it not be better to go for a 40A MCB and 6mm2 cable?
Many thanks
W.
Many thanks for your reply.
So diversity makes the assumption that one will not “max out” the circuit and if they do, the design will mean the circuit breakers will trip. With regard to a ring main, with multiple 13 amp sockets, that assumption make perfect sense and of course reduces costs.
With regard to the cooker, the manufacturer has also applied diversity, somewhat greater than the regs suggest, but in essence, the manufacturer is suggesting that one will not run the oven, grill and all four burners at the same time. I would argue this scenario should be catered for. Think Christmas lunch. Or is it a case that the cooker itself cannot handle this?
I notice the manufacture states the fuse should be 32A minimum, so as I am adding a socket, I need to cater for this by increasing the fuse rating.
In the link you provided (BS7671, OSG, Table 1B), when applying diversity for cookers in a domestic installation, diversity is calculate thus: 10A +30% f.l. + 5A (w/ socket).
The manufacturer specifies:
Burners: 1200W, 1700W, 1200W & 1700W (5800W)
Top oven: 1600W
Main oven: 2000W
Connected load: I = P/V = 9400W / 230V = 40.87A
Applying diversity = 10A + 30% x (40.87A – 10A) + 5A = 24.26A
So for arguments sake, let’s say I had the oven on, drawing 2000W, 1x 1700W burner and a 2300W kettle boiling away. The connected load would then be: 8000W/230V = 34A. My MCB has just tripped!
As I have the additional socket, would it not be better to go for a 40A MCB and 6mm2 cable?
Many thanks
W.
Not exactly, the circuit breaker will not trip at 32.1A.
Diversity does not apply to ring final circuits.
The 'Christmas' scenario is an oft used myth.
Are you sure it does not state a 32A supply minimum?
The fuse/MCB is dependent on the cable selected which in turn is dependent on the design current.
The 9.4kW will have been quoted at 240V so a slight reduction -
9400W / 240V = 39.2A - 10 = 29.2A x 0.3 = 8.75 + 10 + 5 = 23.75A
Your maths has gone awry; that is 6,000W but even at 8,000W (33.3A) - It won't.
An MCB will never trip at 113% of its rating; it will take an hour at 145%.
It depends what you mean by better.
If it makes you feel better then do that but there is no need.
In fact, fractionally less than even that if, per convention, one undertakes ones calculations at 230V ...
39.2A at 240V is about 39.2 x 230 / 240 = 37.5A at 230V. Hence after-diversity current (with a socket) at 230V = 10 + (27.5 * 0.3) + 5 = 23.25A.
Kind Regards, John
Does if you have more than 1 - see R9C2 in Table 1B in the OSG.
It's about time you bought the green one.
It is a vast improvement.
I lied; it's just as bad.
Do we get a yellow one if we wait until next year (not far away!)?
Kind Regards, John
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