32A single and 3 phase supplies feeding catering heat lamps via grid fuse modules.

Happy new year to you too, Hz.

Those lamps seem to be just the thing for this weather. :-)

I am a bit confused. Are the lamps on a TP or SP circuit? Are they on their own circuit, or shared with something else? What is the cable from the ceiling to each lamp?

So 20 lamps @ 300 W each = 6 kW. 2 kW/phase? Could they be on a 10 A MCB?

Hi Chris,

My customer,the steel fabricators are told if the commando socket in the kitchen is 3 phase 32A or 1 phase 32A.I then make up a lead with 3 pin or 5 pin commando plug to supply the grid fuse box.If 3 phase ,I may use 3 fuse units and a connector block for the neutral to supply the banks of heat lamps.All lighting circuits are single phase.My concern was if the fuse units are suitable for the 3 phase use?

               Thanks,hz

Chris,

They could be on a 10A mcb,but the grid fuse boxes are smaller and neater than a din rail enclosure.The grid box is mounted on top of the lighting gantry

                                                Hz

Be aware that some designs of 13A fuse holder don't seem that happy for long term operation in a warm environment at anything too close to the full 13A.  -similar problems arise with fused spurs in airing cupboards and some designs of plug almost anywhere . By all means use 13A fuses as short and overload protection for what are in effect single phase lamps on a 3 phase supply, but perhaps aim for 10A or less per fuse steady loading for a long and cool life.

Mike.

Thanks Mike

                     Hz

I see no particular problem using BS 1362 fuses on single phase circuits derived from a 3-phase supply - that's how about 95% of them are used anyway when you consider the DNO side of things as well.

I suspect heat lamps are basically filament lamps though - very similar in principle to the old domestic GLS lamps - and they had a very definite habit of blowing fuses when the lamp came to the end of its life (when the filament broke, a section of filament with definite resistance was momentarily replaced by an arc/plasma with much lower resistance). So there might be an advantage of using something resettable for local overcurrent protection. DIN rail mounted MCBs aren't your only option though - you can get smaller circuit breakers intended to be built into appliances too.

   - Andy.

A few things intended to help ...

First, ambient temperature around the BS 1362 fuses should be limited to 40 deg C maximum, and not exceed 35 deg C mean over 24 hours (this is the stated service conditions in BS 1362). You might also need to consider ambient temperature for the selected cables vs their service conditions ... also that the fuses themselves dissipate up to 1 W of heat at their rated current. As to how much load you might want to put on each fuse, perhaps worth looking at this article: electrical.theiet.org/.../

hertzal123 said:

My customer,the steel fabricators are told if the commando socket in the kitchen is 3 phase 32A or 1 phase 32A.I then make up a lead with 3 pin or 5 pin commando plug to supply the grid fuse box.If 3 phase ,I may use 3 fuse units and a connector block for the neutral to supply the banks of heat lamps.All lighting circuits are single phase.My concern was if the fuse units are suitable for the 3 phase use?

Second, based on this, BS 7671 may not be the correct standard to apply, because it sounds like a pre-manufactured assembly. A suitable product standard should be selected and certified against.

Third, one thing to be aware of, if you are using the BS 7671 approach for overload protection (which, if there are filament-type lamps being used, is perhaps important), C_f for a BS 1363 fuse  is 0.76 (from BS 1362, I2 = 1.9 × I_n). The same would also apply to BS 646 fuses.

Fourth, your installation instructions for the completed product might also want to stipulate what type of backup protection you need from the protective devices in the electrical installation supplying the socket-outlets in the kitchen, to cover the (admittedly very rare) cases where the prospective fault current at the socket-outlet might exceed 6 kA. (BS 1362 fuses have a rated breaking capacity of 6 kA). I was just thinking that in some large sites, such as large shopping centre, airport, etc, there might be cases where the restaurant just happens to be near to the transformer and prospective fault current is unusually high.

Thanks for the informative reply Graham.

                                                          Hz