13 amp spur

[mrloy99]

here goes again 3rd time lucky
3kw load...13amp spur...does this comply.
My thinking is that previously it would have but not now.
previously 3000w/240volt=12.5amp....all ok

now stated voltage is 230 not 240
so
3000w/230volt=13.05amp marginally over

but to me it does not comply....even though the actual voltage hasn't dropped,its still at 240 in real life.

This is in a high rise office block that i am testing(new installation)
What are the experts views?

 

[Baker1988]

Does the 13 amp fuse keep blowing? If not than aslong as the cable that is on the load side of the fcu can handle the 13 amps I dont really see a problem.

 

[Richard Burns]

Theoretically it may not comply if you are absolutely certain that the 3000W load is 3000W and not, say, 2990W.
A 3000W load (based on 230V) would have a resistance of 17.63 Ω and as you say a current of 13.05 A.
However if this were fed from a 3.3m 2.5mm² cable (or a 2m 1.5mm² cable) the resistance of the cable would be 0.06 Ω and this would reduce the current to 13A as the total resistance from the origin (where the pd is located) includes the supply cable.

Edit: Also based on baker's post a 13A fuse has a near infinite trip time up to about 20-25A.......

 

[Octopus]

What IS the 3kw load?

 

[Geoffsd]

previously 3000w/240volt=12.5amp....all ok

now stated voltage is 230 not 240
so
3000w/230volt=13.05amp marginally over

It doesn't work like that.

If the 3000W was quoted at 240V then (for resistive load) both the amperage and wattage will be lower at 230V

 

[Pete999]

Not got OSG or BGB handy but sure I recall anything over 2kw should be on it's own circuit,

 

[nickblake]

Not got OSG or BGB handy but sure I recall anything over 2kw should be on it's own circuit,

Its regulation 433.1.103 appendix 15 .

 

[mrloy99]

What IS the 3kw load?

The load is a 3kw instantaneous waterboiler.(for making tea etc)..and there are about 50 of them being installed in the building.(supplied as a 4mm,20amp radial.)
I'm pretty sure that there wont be a problem,though in the past I have come across burnt out 13amp spurs which were erroneously fitted to control immersion heaters(pre gas days youngsters people used to use them for hot water)
I think they should be using a 20 amp dp(not a big cost difference if any)

Its more the theory I was querying.Says 3kw on the box.

 

[davesparks]

It doesn't work like that.

If the 3000W was quoted at 240V then (for resistive load) both the amperage and wattage will be lower at 230V

*current, power

 

[Geoffsd]

The load is a 3kw instantaneous waterboiler.(for making tea etc)..and there are about 50 of them being installed in the building.(supplied as a 4mm,20amp radial.)
I'm pretty sure that there wont be a problem,though in the past I have come across burnt out 13amp spurs which were erroneously fitted to control immersion heaters(pre gas days youngsters people used to use them for hot water)
I think they should be using a 20 amp dp(not a big cost difference if any)

Its more the theory I was querying.Says 3kw on the box.

All is good, then.

I agree with you about the DP switch; the fuse is not necessary.

 

[bigdavs83]

Anytime I've replaced a burnt out spur for an immerser it's been a 20a dp switch that's fitted. Just for that reason of the spurs being too close to the kW rating.

 

[Geoffsd]

*current, power

Yes, I know that, thank you.

I was keeping it in the same language as the question, just in case.

 

[davesparks]

Just in case of what?

 

[Geoffsd]

What's the problem?

Just in case anyone didn't know.

wattage: definition of wattage in Oxford dictionary (British & World English)
amperage: definition of amperage in Oxford dictionary (British & World English)

 

[davesparks]

What's the problem?

Just in case anyone didn't know.

wattage: definition of wattage in Oxford dictionary (British & World English)
amperage: definition of amperage in Oxford dictionary (British & World English)

Read the definition of amperage that you have just linked to.

It defines it as the strength of an electric current, not as being the same thing as the current! Could you possibly share with us the formula used to define this and the unit?