Light problem.

[ericmark]

421.1 Electrical equipment shall not present a fire hazard to adjacent materials.
Manufacturers' instructions shall be complied with.

OK maybe now withdrawn with 18th edition, but for years we had to follow it.

 

[bernardgreen]

A 100 Watt incandescent lamp has a cold resistance of 40 Ohms. Apply 230 Volts to the lamp and the initial current is 5.75 Amps

5.75 Amps and 230 Volts is 1.32 kW

When the filament is white hot the resistance is about 540 Ohms ( Calculated )

230 Volts and 540 Ohms produces a current of 0.42 Amps.

Hence the "inrush" current to the cold lamp is about 14 times the running current.

Anything that controls the lamps therefore has to be capable of switching 14 times the rated current for several milliseconds.

 

[JohnW2]

421.1 Electrical equipment shall not present a fire hazard to adjacent materials.
Manufacturers' instructions shall be complied with. OK maybe now withdrawn with 18th edition, but for years we had to follow it.

I can't find quite that in either 17th (Amd3) or 18th, but the 18th does have:

421.1.1 Persons, livestock and property shall be protected against harmful effects of heat or fire which may
be generated or propagated in electrical installations.
Manufacturers’ instructions shall be taken into account in addition to the requirements of BS 7671.

However, they are extremely vague, and say absolutely nothing about over-current protection.

Do you seriously believe that the difference between a ceiling rose being 'protected by' a 6A or 16A OPD makes any noticeable difference to the degree of "fire hazard to adjacent materials", or whatever?

Kind Regards, John

 

[JohnW2]

Anything that controls the lamps therefore has to be capable of switching 14 times the rated current for several milliseconds.

I can't fault your arithmetic, but I'm not sure what side of the argument (about the rating of the OPD protecting a lighting circuit) this puts you on

Theory and practice seem to differ, perhaps because the "several milliseconds" is, in reality, a very small number of milliseconds. By your figures, switching on 6 x 100W incandescents from cold should immediately magnetically trip a B6 MCB - but it doesn't!

Kind Regards, John

 

[ericmark]

I knew there was a change "shall be taken into account" was added on one of the 17th edition amendments, you can now use some common sense when you think the manufacturer is wrong.

I did say

OK maybe now withdrawn with 18th edition, but for years we had to follow it.

As to @bernardgreen post, yes I know we would put a row of 3 switches for one room, as all on one it could trip an MCB but the few seconds between switching on the 3 switches was enough to ensure total did not exceed the 30 amp a type B would allow, was not required with the old fuses.

I have not looked at an LED, since a capacitor is used as a current limiter there still could be an inrush, I missed that day at college.

 

[bernardgreen]

switching on 6 x 100W incandescents from cold should immediately magnetically trip a B6 MCB - but it doesn't!

Ha been known to. ( maybe a few more than 6 lamps )

Where lamps are being switched frequently ( such as stage lighting, animated illuminations and lamps on large mimic displays ) the lamps can be kept "warm" by resistors or capacitor in parallel with the switch passing enough current to keep the filaments warm.

 

[JohnW2]

Ha been known to. ( maybe a few more than 6 lamps )

Per the arithmetic, 6 x 100W should be enough, even if the B6 requires 5In to trip magnetically. If it tripped at 3In (still within spec), 4 x 100W ought to be enough.

I've never personally experienced that situation 'in normal use'. The closest I got was that I once had a room with a total of 18 x 25W candle bulbs (i.e. 450W), all controlled by a single switch - and that certainly never tripped a B6 at switch-on. However, back it those days, it's quite likely that more than a total of 600W of incandescent lighting on one B6 circuit will have been 'on' when a power cut (common in these parts!) occurred, so all will have come back on simultaneously when power was restored - but I don't recall a trip ever having occurred when that happened.

It was, of course, when incandescent bulbs died that the MCB would very commonly trip!

Where lamps are being switched frequently ( such as stage lighting, animated illuminations and lamps on large mimic displays ) the lamps can be kept "warm" by resistors or capacitor in parallel with the switch passing enough current to keep the filaments warm.

That makes sense.

Kind Regards, John

 

[Joeydeacon]

Hi JohnW2. Thanks for the other pic you sent. Just got round to looking at the consumer unit which feeds the cabin and this is what is supplying it. Is it possible to run a spur from a socket like was asked in the original comment? Thank you.

 

[Harry Bloomfield]

View attachment 211787 Hi JohnW2. Thanks for the other pic you sent. Just got round to looking at the consumer unit which feeds the cabin and this is what is supplying it. Is it possible to run a spur from a socket like was asked in the original comment? Thank you.

Yes!

 

[JohnW2]

Yes!

Strictly speaking, Yes provided that the socket is not already a spur from a ring final circuit (which I imagine/presume it isn't).

Kind Regards, John

 

[SUNRAY]

Ha been known to. ( maybe a few more than 6 lamps )

Where lamps are being switched frequently ( such as stage lighting, animated illuminations and lamps on large mimic displays ) the lamps can be kept "warm" by resistors or capacitor in parallel with the switch passing enough current to keep the filaments warm.

10x 100W will commonly trip a B6, ask any AmDram lighting tech...