Power Loss/Pole of 16A MCB

In a single phase circuit the current in the line and neutral will be equal, so the power loss will be 2 x 2.6W.

That power loss would be the case were an overload disconnect arrangement fitted to the neutral, which seems unusual though not impossible; such an arrangement is prohibited under British Standard 7671. The original poster has not discussed this yet.

Don't have the regs. to hand (working from home), but I think such an arrangement is permitted provided that the line and neutral switching functions are mechanically linked (and the connections through the MCB are the only possible route for power to the downstream circuits). Please correct me if I'm wrong.

That would make sense, with current overload detection in the phase (only) disconnecting the phase and the neutral as well. That would be safe.

If a 2-pole MCB had overcurrent detection on just one of the poles, you would expect the neutral pole to be marked. This is the case with 2-pole RCBOs, where the neutral is clearly marked and overcurrent detection on just the phase pole.

I'm not claiming to have seen 'em all, but all of the 2-pole mcbs that I have seen are like two single-pole mcbs clipped together with a pin linking their trip mechanisms so one tripping pops the other as well, and with no marking to indicate that one pole should be used as a neutral.

Where do you get this MCB power loss from?

Some power will be lost in the overload sensing arrangement.

Sorry, I meant to ask the OP, how did power loss figure was obtained, by measurement or from data sheet? Seems quite high to me . When I touch the MCB, it is not warm to touch, does not feel like it is dissipating 2.6 W.

I suspect the 2.6W is worst-case, based on the max. contact resistance and (as PW said) the tripping circuit impedance, all taken at the full current rating.

Quite.

A quick check of the datasheet that I have on hand for (GE) MCBs gives a dissipation per pole for a 16A MCB of 2.57W, so the OP quite correct.

Bear in mind that this is the dissipation at 16A. Any MCB that you are likely to encounter in a working situation will be carrying less than its rated current, with the heating varying with the square of the current.

I have bench-tested MCBs at their rated current to assess their tripping performance, and can confirm that they do get rather warm - terminals at 30-40 degrees C above ambient would not be unexpected, nor would it be any cause for concern.

GA, I was hoping someone will confirm it.

Quite a good and informative discussion. The max power loss is given by the manufacturer in the catalogue. Sometimes the neutral does not have any protective devices like thermal and magnetic elements. The bimetal and the heater cause the maximum heat loss. So, the P+N may not consume as much as 2P.

However, if the user used a normal 2P MCB, the loss can be 2X2.6=5.2W.

what i have used is schnedier electric multi 9 MCB C60H 2P.....that means the total power dissipated is 5.2W. if this is the case , then a 3phase (4 pole) MCB will dissipate 2.6x4 W . am i right?

Yes, a 2 Pole Multi 9 MCB has protection in both poles, so the power loss when carrying the rated current will be a maximum of 2.6W per pole. Actual figures can be as low as 2W per pole, since a reputed manufacturer like Schneider will publish a pessimistic figure here.

A 4 Pole MCB will have the same loss per pole, but if the load is balanced, there will be no current and hence no loss in the pole which is used as the neutral. 3X2.6W is more realistic in this case.

thanks a lot............

Interesting. I was involved in a project a LOOOOOONG time ago when solid state overload relays were first coming out, and we tested bi-metal OLRs to make a comparison of energy losses. We consistently came up with roughly 3W per RLA on a bimetal strip, 4W per RLA on a eutectic melting alloy type. So those numbers were significantly higher than what you are seeing here. I guess CB bi-metal strips must be, by necessity, much more efficient.