What if someone told you that they wanted to plug a 2kW (@240V) fan heater into each socket and turn them all on at once for 5-10 minutes?
New Wiring for separate Hob & Double Oven
- Thread starter Stu1H
- Start date
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H
holmslaw
..
OK.
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according to the curves in the regs, a B20 breaker will take 40A for about 180 seconds before it blows..
a lot of damage can be done in 3 minutes at twice the rated current..
granted the copper won't melt ( and maybe I should choose my words more carefully in future ) but the insulation won't like it..
Thanks for all your guidance Col, this is what i'm going to do. Up the MCB to 50A, 10mm cable from CCU to double cooker outlet and I've found a decent double oven and hob which total 11.7kw (pretty much bang on 50A) ......
... however i do need some more advice on the new MCB as I just read somewhere that the council (my house is ex council) used a lot of Wylex CU's in the 80's and 90's which are now difficult to find MCB's for.
The MCB says B40 (at the top) and NSB40 at the bottom. So from I can tell it looks like I need an SP Type B Curve MCB. Can you confirm this is correct.
Cheers
... however i do need some more advice on the new MCB as I just read somewhere that the council (my house is ex council) used a lot of Wylex CU's in the 80's and 90's which are now difficult to find MCB's for.
The MCB says B40 (at the top) and NSB40 at the bottom. So from I can tell it looks like I need an SP Type B Curve MCB. Can you confirm this is correct.
Cheers
H
holmslaw
..
I have made no such mistake
I suggested right from the get go that he should install a seperate supply for the oven.
I also never advised him to change the breaker.
I pointed out that the combination of the 2 appliances would exceed the current breakers rating to emphasise the point that a new feed is required for one of the appliances.
YOU then tried to tel the OP that he's ok sticking 12.5KW of equipment on a circuit that is not capable of it by citing diversity and I tried to point out that diversity doesn't count when designing the circuit..
I suggested right from the get go that he should install a seperate supply for the oven.
I also never advised him to change the breaker.
I pointed out that the combination of the 2 appliances would exceed the current breakers rating to emphasise the point that a new feed is required for one of the appliances.
YOU then tried to tel the OP that he's ok sticking 12.5KW of equipment on a circuit that is not capable of it by citing diversity and I tried to point out that diversity doesn't count when designing the circuit..
But all that is taken into account in the required relationship of Ib to In to Iz, and a cable with an Iz of 20 is OK on a breaker with an In of 20.
It may be on the limit, but it is not against the regulations.
H
holmslaw
..
H
holmslaw
..
as for 311.1..
Part 3 is "assessment of general characteristics".
as I read this, the installation as a whole is to be assessed and you can use diversity to determine the "average useage" of items within the installation.
not all lights will be on all the time, not every socket will be in use all the time, the shower will not be on all the time, the cooker will not be on all the time, etc..
now, please note the word "may" in the regulation.. this means that you do not have to apply diversity if you so wish.. it's up to the designer of the circuit.
also please note that the regulations themselves do not stipulate what percentage of use you use for each circuit, and even the OSG says that it's up to the designer to decide what to apply, the figures given in the table are guidelines only..
so I stand by my declaration that diversity is for the whole installation demand and not for determining the design characteristics of a single circuit within that installation..
for every circuit the following MUST be true..
or in simpler terms Ib ≤ In ≤ Iz..
where
Ib is the design current for that circuit
In is the current rating or current setting of the protective device
Iz is the current rating of the cable
Part 3 is "assessment of general characteristics".
as I read this, the installation as a whole is to be assessed and you can use diversity to determine the "average useage" of items within the installation.
not all lights will be on all the time, not every socket will be in use all the time, the shower will not be on all the time, the cooker will not be on all the time, etc..
now, please note the word "may" in the regulation.. this means that you do not have to apply diversity if you so wish.. it's up to the designer of the circuit.
also please note that the regulations themselves do not stipulate what percentage of use you use for each circuit, and even the OSG says that it's up to the designer to decide what to apply, the figures given in the table are guidelines only..
so I stand by my declaration that diversity is for the whole installation demand and not for determining the design characteristics of a single circuit within that installation..
for every circuit the following MUST be true..
or in simpler terms Ib ≤ In ≤ Iz..
where
Ib is the design current for that circuit
In is the current rating or current setting of the protective device
Iz is the current rating of the cable
Don't understand coljacks comment about not allowing diversity on final circuit?
OSG page 96 "household cooking appliance"
First 10A of rated current plus 30% of remainder plus 5A if socket outlet on control unit!
Diversity for cookers has been allowed since 14th ed. at least, slight variations but always there, even at main festive seasons thermostats still work to ensure individual rings etc. not all on at same time.
OSG page 96 "household cooking appliance"
First 10A of rated current plus 30% of remainder plus 5A if socket outlet on control unit!
Diversity for cookers has been allowed since 14th ed. at least, slight variations but always there, even at main festive seasons thermostats still work to ensure individual rings etc. not all on at same time.
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