School system overloaded?

[JakeWest88]

Current issue that needs to be resolved:

 

We currently have around 20 - 25 tungsten generics in a black box theatre all ran off 5amp sockets in the air but then terminating into the dimmers (zero 88 betapacks) at 15amp sockets. Most of these generic fixtures are 150 - 300watts of light output.

 

Recently the school have put up a selecon fresnsel which to my knowledge has a 1200watt lamp inside of it. Recently the socket that it terminates to in the dimmer room keeps blowing fuses.

 

I'm thinking that it's because the light is too powerful? Or is there anything else is could be?

[sleah]

Current issue that needs to be resolved:

 

We currently have around 20 - 25 tungsten generics in a black box theatre all ran off 5amp sockets in the air but then terminating into the dimmers (zero 88 betapacks) at 15amp sockets. Most of these generic fixtures are 150 - 300watts of light output.

 

Recently the school have put up a selecon fresnsel which to my knowledge has a 1200watt lamp inside of it. Recently the socket that it terminates to in the dimmer room keeps blowing fuses.

 

I'm thinking that it's because the light is too powerful? Or is there anything else is could be?

In a nutshell, I think you are correct. 1200w is right on the limit for 5amps and it's likely that the fuse is (quite rightly) 5amp.

Presumably the fuse you refer to is on the dimmer pack?

Short of upgrading the cabling from the dimmers to the lighting bars, I'm afraid you're out of luck.

Do NOT be tempted to replace the fuse with anything above 5amps as very bad things could happen - such as melting cables and plugs!!

[kgallen]

Betapack channels usually have 10A 1.25"/32mm HRC fuses. In this case it seems they may have been downrated to 5A - rightly so with the 5A lighting bar distribution described. However this is worth checking, since if the Betapacks are still equipped with 10A channel fuses then there is a more serious problem somewhere in that cabling.

 

The other explanation is that in addition to the Selecon 1200W, there is another fixture also plugged into or paired on that channel. Most Betapacks have twin 15A socket outlets per channel, so if the Selecon 1200W is on one outlet and one of the 150W/300W on the other outlet - with the channel fuses at 5A - then that demand is somewhat over 5A.

 

The Selecon on its own is slightly over 5A, so even if the above applies, running the Selecon 1200W on that infrastructure is marginal at best and even if it can be made to work as the only fixture on one channel, it's quite possible a 5A fuse will fail some time in the middle of a production. I don't have the I-t curves for a 5A HRC fuse, but a 5A BS1361 fuse would carry 5.2A (1200/230) for pretty much forever, but a weak or old fuse could blow at an inconvenient time.

 

I think a knowledgable review of that circuit is needed wrt fuse ratings in all channels and what fixtures are connected to those channels.

 

Kevin

Edited June 18, 2021 by kgallen

[adam2]

I would be very surprised indeed if a 1,200 watt lamp is regularly blowing a 5 amp fuse. The degree of overload is very small.

It is possible that some other fault or overload exists. More details required.

 

A 1,200 watt lamp designed for 240 volts and used on a 240 volt supply is exactly 5 amps.

A 240 volt lamp used on a 230 volt supply is slightly less than 5 amps.

Edited June 18, 2021 by adam2

[Dave m]

aren't they normally 650? Are they Aclaims?

 

One obvious solution is to run the lamp with a lower lamp anyway.

a 1200w light is going to stick out if all your other lights are on the low side.

 

The Rama is 1200 but would normally have a 15A feed

Edited June 18, 2021 by Dave m

[kitlane]

I would be very surprised indeed if a 1,200 watt lamp is regularly blowing a 5 amp fuse. The degree of overload is very small.

It is possible that some other fault or overload exists. More details required.

 

A 1,200 watt lamp designed for 240 volts and used on a 240 volt supply is exactly 5 amps.

A 240 volt lamp used on a 230 volt supply is slightly less than 5 amps.

 

Would inrush current to a cold filament be enough to tip it over the edge, or would the fuse cope because it is HRC?

[kgallen]

Betapacks have preheat so unless the channel is slammed to max at time 0 the filament shouldn’t be cold.

[Don Allen]

You can change the Rama from a 1200W to a 1000W lamp to reduce the current drawn, but you need to change the lampbase height to suit the different filament Rama manual .

[sunray]

At school we had a Strand 2KW fresnel, our circuits were fused at 7A (No idea of characteristics in thse days) I don't recall ever blowing a fuse even when it was paired with a 500W. All of our cabling was 3/0.029" and 5A plugs/sockets.

 

More recently I've run HMI's on 4A fused dimmer packs without issue.

 

 

 

Are you always on the same dimmer channel? could be a faulty fuseholder overheating.

 

[gareth]

At school we had a Strand 2KW fresnel, our circuits were fused at 7A (No idea of characteristics in thse days) I don't recall ever blowing a fuse even when it was paired with a 500W. All of our cabling was 3/0.029" and 5A plugs/sockets.

 

More recently I've run HMI's on 4A fused dimmer packs without issue.

 

 

Not sure where to start with that one....

[themadhippy]

7a fuses were the fuse of choice for old green ginger 2kw packs,and is a sensible choice if you look at the IT graph.

All of our cabling was 3/0.029"

or roughly 1.5mm so more than adequate for 7A,just the connectors used is a bit underrated,but no different to the multitude of 16A sockets being protected by a 20A device

[sunray]

At school we had a Strand 2KW fresnel, our circuits were fused at 7A (No idea of characteristics in thse days) I don't recall ever blowing a fuse even when it was paired with a 500W. All of our cabling was 3/0.029" and 5A plugs/sockets.

 

More recently I've run HMI's on 4A fused dimmer packs without issue.

 

 

Not sure where to start with that one....

 

If you look at fuse curves, nothing is designed to rupture at full rated current plus a tiny bit, as an example a BS1362 fuse at 10000 seconds requires roughly a 50% overload. On that basis 2KW at ~8.3A is well inside the 7A + 50% or 1.2KW at ~5.3A is under 4A + 50%.I'll add that this is not the way I plan to work and the recent HMI's on 4ch packs with 4A fuse I only knew about after operating the 3 shows and ripping out.

 

 

[Junior8]

There will be many educational settings where 5A was fitted as the assumption when the installation was done was that 500W lanterns would be standard. I wouldn't mind betting that originally the patch would have been 5A as well maybe even to a couple of Junior 8s. Even in 1990 when I last was involved in fitting out such a space my specification of 15A and suitable cabling caused more than a raised eyebrow amongst the drama advisory staff who couldn't see that the increasing availability of 650W at reasonable prices would lead quickly, as it did, to 1000W affordability and that would mean that 5A would soon be non-standard in control. Had I not been there it would have been 5A.

 

In this case I would not make any assumptions on the wiring simply on the basis of what is fitted at the patch. If this lantern is continually blowing fuses - and the circuit has been checked with a lower power lantern and proved to be OK - then stop using it and get someone in to check what the spec of the whole system is. They might well find it enlightening.

 

In any school with 5A outlets assume is was designed for max 650W lanterns.

Edited June 18, 2021 by Junior8

[adam2]

I repeat my earlier remark that a 1,200 watt lamp is unlikely to regularly blow a 5 amp fuse.

 

However SOMETHING is clearly operating the fuses. And further investigation is prudent. In particular the following points.

 

A PROPER test and inspection of the lantern that is blowing fuses. Confirm by inspection that the lamp is in fact 1,200 watt, and not some larger lamp that has been bodged to fit. Careful inspection of the plug, the flexible cord and the internal wiring of the lantern. Replace if in doubt.

 

Confirm by inspection that the blown fuses are in fact 5 amps and not some smaller size. School installations are prone to having smaller fuses fitted "for improved safety"

 

Double check for any wrong or mistaken patching. A 1,200 watt lantern sharing a channel with another small lantern could well blow a 5 amp fuse.

 

A formal test and inspection of the wiring between the dimmers and the lanterns.

[Jivemaster]

IN my old school the stage lighting circuits were often run to pairs of sockets. This was fine when 250w and 500w lamps were the norm but start adding a 1000w lamp and running it's pair with a 500w then something would get warm.