cable and circuit breaker size for single oven

[mactech]

Hi there
Would very much appreciate help with selecting suitable cable and breaker size for new single oven reated at 2.8kw as a radial circuit.

The current cable installed to my single oven (2.8kw) is 4mm twin and earth approx 15 meters, clipped to joists above ceiling space. No other cables in proximity. This radial circuit is connected to 32amp breaker in modern CU.
Could you please advise on using 4mm or 6mm cable and what size trip breaker to use. I think a 20amp would be more suitable. No other kitchen equipment will be connected to this circuit.

Thanks[/youtube]

 

[EFLImpudence]

You do not need to alter anything.

Use 4mm² flex to connect the oven,

 

[phatboy]

Yes a 20amp breaker would be fine, although the 32amp isn't unsafe.

The oven is only using about 12amps.

 

[JohnW2]

Hi there
Would very much appreciate help with selecting suitable cable and breaker size for new single oven reated at 2.8kw as a radial circuit. The current cable installed to my single oven (2.8kw) is 4mm twin and earth approx 15 meters, clipped to joists above ceiling space. No other cables in proximity. This radial circuit is connected to 32amp breaker in modern CU.
Could you please advise on using 4mm or 6mm cable and what size trip breaker to use. I think a 20amp would be more suitable. No other kitchen equipment will be connected to this circuit.

I take it that you are replacing one 2.8 kW oven by another 2.8 kW one, not having both?!

4mm² cable is more than adequate for your oven. The 32A breaker (which is really only there to protect the cable) is also appropriate and perfectly OK for 4mm² cable installed as you describe but, as you observe, a 20A (or even 16A) one would be adequate from the point of view of the power requirements of your oven. If you want to play things by the book, the oven manufacture may specify what size breaker should protect the circuit (and may try to claim that your warranty will be invalidated if you don't comply!).

Kind Regards, John

 

[mactech]

Thanks to everyone for your replies. Forgot to mention that I am replacing a 2.8kw single oven with a new 3.5kw single oven, I assume the current 4mm cable is still adequate with a 20amp breaker

thanks again

 

[EFLImpudence]

Forgot to mention that I am replacing a 2.8kw single oven with a new 3.5kw single oven, I assume the current 4mm cable is still adequate with a 20amp breaker

Yes, but you do not need to replace the breaker.

However, if you wish to replace it because of lack of knowledge - no disrespect - because you think it 'safer' then logically you should replace it with a 16A one in which case 1.5mm² flex could be used.

 

[JohnW2]

Yes, but you do not need to replace the breaker. ... However, if you wish to replace it because of lack of knowledge - no disrespect - because you think it 'safer' then logically you should replace it with a 16A one in which case 1.5mm² flex could be used.

Quite so ...

4mm² cable is more than adequate for your oven. The 32A breaker (which is really only there to protect the cable) is also appropriate and perfectly OK for 4mm² cable installed as you describe but, as you observe, a 20A (or even 16A) one would be adequate from the point of view of the power requirements of your oven.

One should perhaps add that there is absolutely nothing electrically wrong with having a breaker of lower rating that would be possible with the cable concerned,provided that the rating is adequate for the load. Indeed, having a lower-rated breaker increases the chances that a 'reduced-csa-flex' at the end of the circuit would have adequate fault protection (and, as you say above, maybe even adequate overload protection).

Kind Regards, John

 

[EFLImpudence]

One should perhaps add that there is absolutely nothing electrically wrong with having a breaker of lower rating that would be possible with the cable concerned,provided that the rating is adequate for the load.

No obviously not, nor anything wrong with having a larger cable than required which it would then be?

Indeed, having a lower-rated breaker increases the chances that a 'reduced-csa-flex' at the end of the circuit would have adequate fault protection

It wouldn't then actually be a reduced-csa-flex.

(and, as you say above, maybe even adequate overload protection).

It would even though still not possible.

 

[JohnW2]

Indeed, having a lower-rated breaker increases the chances that a 'reduced-csa-flex' at the end of the circuit would have adequate fault protection

It wouldn't then actually be a reduced-csa-flex.

Well, if it's reduced-csa (i.e. if csa reduces at some point in the circuit), then it's reduced-csa, but I think I know what you meant. If, as with the figures we were considering, even the downstream 'reduced csa' (compared with the cable upstream of the 'join') is getting adequate overload protection from the OPD, then that's a fait accomplis. However, I was speaking more generally ... in a situation in which the downstream cable (usually flex) is not getting adequate overload protection from the circuit's OPD, having an OPD of as low as possible a rating (consistent with the load) presumably increases the chances that the flex will have adequate fault protection.

(and, as you say above, maybe even adequate overload protection).

It would even though still not possible.

You've rather lost me there. As you said, a 16A MCB would give adequate overload protection to 1.5mm² flex. What's "not possible"?

Kind Regards, John

 

[EFLImpudence]

What's "not possible"?

A 12A oven to overload an adequate cable.

 

[JohnW2]

What's "not possible"?

A 12A oven to overload an adequate cable.

Oh, I see. Yes, fair enough - but, as I said, the important point is that having an OPD rated less than the cable could 'stand' increases the chances that there would be adequate fault protection for any cable beyond a reduction in CSA.

Of course, as previously discussed, the same argument would allow us to reduce to entire cable run (from CU to oven) to 1.5mm² and, provided that fault protection could be shown to be adequate, protect it all with a 40A MCB.

Kind Regards, John