MCB for 9.5kw shower

[FiremanT]

I am changing an electric shower for my daughter in the morning. The old unit is a 7.9Kw. the cable is 10mm. The existing breaker is a Hagar type B MTN140. Hagar appear not to do a 45A, but it appears, from other old forum responses, that the existing 40A will be okay.

Am I correct in deducing that the 40A is okay, and is better than fitting a 50A?

I am hoping to get a definitive response this evening - I can get a 50A in the morning if that is the preferred option. But I could do without travelling out of my way to get one if not required.

Thanks

 

[EFLImpudence]

Mistake.

 

[EFLImpudence]

Oh I'm sorry.

Don't know why but I was thinking of 10.5kW.

40A will be fine.

 

[EFLImpudence]

Fireman, did you see my correction?

Sorry again.

 

[FiremanT]

Fireman, did you see my correction?

Sorry again.

Thanks, EFL. I would not have seen this if you had not PM'd. Cheers.

 

[Risteard]

50A would be far better. A 40A will be running very close to capacity if the 9.5kW has been calculated at 240V rather than the correct nominal voltage of 230V - in which case it will be running above capacity.

A 40A is not the correct device to use for this - but an Electrician is required to change this, having due consideration for the suitability of the existing installation for the change in rating etc.

 

[FiremanT]

50A would be far better. A 40A will be running very close to capacity if the 9.5kW has been calculated at 240V rather than the correct nominal voltage of 230V - in which case it will be running above capacity.

A 40A is not the correct device to use for this - but an Electrician is required to change this, having due consideration for the suitability of the existing installation for the change in rating etc.

It is a new Mira Sprint, so would that not be calculated at 230V?, I will have a look. The house was built about 5/6 years ago.

 

[FiremanT]

Right, I have done what I should have earlier: checked the MI's! I thought it was 45A, based on my calculation, although very close to 40.

The MI's state the recommended MCB is 40A.

@240v = 9.5Kw
@230V = 8.7Kw

Thanks again for responding

Edited 9.5 from 9.6 (‘‘twas late. )

 

[EFLImpudence]

The 9.5kW will be at 240V which is 39.6A.

At 230V it would be 8.74kW and 38A.

39.6 is less than 40 so...

 

[EFLImpudence]

A 40A will be running very close to capacity

Please state how close to capacity complies with ≤.

 

[Risteard]

Please state how close to capacity complies with ≤.

A shower is a fixed load. It cannot overload.

Some national standards actually prohibit designing an installation to run at the full rated load of such devices as this generates heat.

 

[JohnW2]

Some national standards actually prohibit designing an installation to run at the full rated load of such devices as this generates heat.

If that is/were the case, then the same nations' Standards really ought to require that the stated 'rating' of an MCB was such that drawing that current continuously through it would does not result in an unacceptable amount of heat being generated.

What on earth would be the sense of 'rating' a device at "X maximum" if that had to be interpreted as meaning that the maximum permissible current was something less than X?

Kind Regards, John

 

[EFLImpudence]

A shower is a fixed load. It cannot overload.

I know. What has that got to do with it?

You said, in effect, that 39.6A was too close to 40A for it to be acceptable and I asked how much less than 40A would be acceptable when the regulations state that 39.6 ≤ 40A complies and is satisfactory even if the appliance could cause an overload.

Some national standards actually prohibit designing an installation to run at the full rated load of such devices as this generates heat.

I do not know if that is true but in any case ours do not.

Isn't that what fusing factors are and why OPD devices do not get too hot at their rated current and do not blow/trip at 101% of their rating.

So, your claims are incorrect and irrelevant.