45 AMP MCB'S

[JohnW2]

The heat inside a distribution board where all the MCB’s are near their limit is rather high they all produce heat and that heat has to go some where.

It would be but, in a domestic environment (and many a commercial one), one is simply never going to get anywhere near that position ("all MCBs near their limit") for a significant period of time. As has been said, the average total current demand from a domestic CU is generally going to be under 10A, regardless of the number and ratings of the MCBs. IIRC, DNOs work on the basis of about 2.5kW average for normal deomestic properties.

Let's face it, an average demand of 10A (2.3kW), for just a modest 12h per day (assumed zero demand for the other 12 hours) would cost around £1600 per year.

It is reported that there have been many consumer unit fires so I can see how manufacturers would want to limit the sizes of the MCB’s fitted.

Facts are very hard to come by, but I would strongly suspect that a very high proportion of fires which originate in CUs are due to poor connections, not to MCBs etc. bursting in flames because of overheating due to their carrying high currents at a high ambient temperature.

Kind Regards, John

 

[kai]

There is one situation where breakers will run at higher load for seven hours every night - economy seven, when all the storage heaters are charging up during night time off peak hours.

 

[JohnW2]

There is one situation where breakers will run at higher load for seven hours every night - economy seven, when all the storage heaters are charging up during night time off peak hours.

Probably not as much as you would think - just do the sums. If several MCBs were carrying current close to their rated value continuously for 7 hours per night, than even at E7 off-peak rate, that would probably cost a fortune!

Kind Regards, John

 

[RF Lighting]

Never heard of thermostats?

 

[JohnW2]

Never heard of thermostats?

I presume that wasn't directed at my last post, since that was my very point!

Kind Regards, John

 

[RF Lighting]

No it wasn't, it was to our resident Wylex rep.

 

[kai]

Yes the thermostat will cut in and out after the initial heat up from cold takes place. Imagine in a block of flats where the storage heaters come on at say midnight, there will be an hour or two of full load on all heaters, as the cool bricks charge up, gradually the thermostats will start to control the demand, by cutting in and out at intervals.

 

[RF Lighting]

But you just said the circuit breakers will be on full load for 7 hours. I think most of us know how storage heaters work.

 

[kai]

Oops - a small error there.

 

[EFLImpudence]

Why is the supply on for seven hours then?

 

[kai]

Economy Seven Supply, is normally available for seven hours from when the Board's timeswitch cuts in, until it cuts out in the morning.

 

[EFLImpudence]

Yes I know that, but if it only takes a couple of hours to heat the bricks then 5am to 7am would be better.

Perhaps I don't know how storage heaters work -
How long does it take to heat the bricks - fully - to maximum temperature and what is that maximum temperature?

 

[JohnW2]

Yes I know that, but if it only takes a couple of hours to heat the bricks then 5am to 7am would be better.

Yes, that could be true - but it's really the user's problem. The suppliers provide cheap electricity during the hours of low network demand, not for the period required by the consumer's loads, and it's up to the users to make use of that cheap electricity in whatever way they see fit.

IF (and I haven't a clue) it were the case that the bricks could be heated to full temperature in a couple of hours (indeed, anything less than 7 hours) then, as you say, it would make sense to power the heaters only for the required amount of time at the end of the cheap-rate period - and the user is free to install their own time switches to achieve that.

Perhaps I don't know how storage heaters work - How long does it take to heat the bricks - fully - to maximum temperature and what is that maximum temperature?

As above, I haven't got a clue, either. However, if one did know the answer, then, again as above, it would make no sense to start powering the heaters any earlier than was necessary for the bricks to reach their 'full temperature' by the end of the cheap-electricity period.

Kind Regards, John

 

[kai]

In very colder weather it usually takes longer heating in order to bring the bricks up to the desired running temperature. In Spring and Autumn it takes less time to do so. There is a knob on the top of the heater to set for Snowy weather, Cold weather, or Mild weather (or similar), which will adjust the thermostatic circuits accordingly. In one local authority Cyclo-Control system, the heater knobs were recommended to be left on the Snowy setting, and a Clunky Cyclo-Control time switch was used to control the time the power was fed to the Off-peak Board, depending on prevailing weather conditions, as measured by duplicated sensor equipment mounted on the roof of the tower block. This system worked very well, as the tenants never had to worry about setting the thermostats correctly.
In winter, the loud CLUNK as the offpeak feed came in was about midnight, in milder weather, the offpeak on CLUNK could have been around Three in the morning as far as I can remember. The morning OFF CLUNK was always about Seven in the morning though.

 

[JohnW2]

In very colder weather it usually takes longer heating in order to bring the bricks up to the desired running temperature. In Spring and Autumn it takes less time to do so. There is a knob on the top of the heater to set for Snowy weather, Cold weather, or Mild weather (or similar), which will adjust the thermostatic circuits accordingly.

I don't really understand why the thermostat should need adjusting according to the ambient temperature, unless you're suggesting that the bricks are heated to a lower temperature when the weather is warmer. What would make sense (per the system you go on to describe) is to delay the start of powering the storage heaters during warmer weather - the last thing one wants to do is to unnecessarily get the bricks 'up to temperature' (even if that temperature is lower when the weather is warm) hours before they need to be!

Kind Regards, John