3-phase worries for football stadium audio equipment racks

[AudioExpert]

I was recently surveying a football stadium and the amplification racks for two of the stands were in one location. The equipment was mounted in 3 separate racks each housing about eight 400 watt amplifiers (real long term power not home hi-fi peak/transient power)

This makes for quite a current draw: at full tilt each rack would probably draw about 15 amperes.

When I checked the electrical feeds to each rack I found that each rack was fed from a different electrical phase.

Commercial amplifiers need a large mains transformer so present an inductive load so I can sort of understand the need to balance it.

My concern was that there could be large potential difference between the racks which could be quite scary - all the racks are next to each other with low voltage and current signal cables running between them.

Is this set-up a concern or am I being overly cautious.

If this is dangerous are there any ways to reduce the dangers without needing to rewire.

Nigel

 

[Edd]

All the electronics will be run from step down transformers, giving you isolation of a kind. The only time you are likely to see 400V is on the power supply side, between pannels but these should be sealed and seprated from from the LV side. if you open the back of 2 panels you will see 400v but you should have the aproprate lables stuck on them with a warning.

 

[plugsandsparks]

No problem and no different to TP going to a control panel, as already mentioned BS7671 covers this with warning labels "400V" etc to be put on the outside of the racks.

 

[AudioExpert]

Thanks Edd when you say panels do you mean the racks or the individual amplifiers?

 

[DNS1]

I understand your concerns about cross-phase faults, but I'm a bit confused as to why they've chosen to do this in the first place!

I worked as a sound technician for many years and we ALWAYS ran ALL the amps (on our systems, these sometimes drew in the region of 100A!) on the same phase (where I was, the blue phase, as it was at the time, was always for sound gear, the red and yellow were for the horrible lighting techies!)

15A per rack really is nothing, just a little more than a decent domestic kettle.

As I understand, to comply with the regs you just need to stick the 400V stickers on the racks.

 

[plugsandsparks]

Thanks Edd when you say panels do you mean the racks or the individual amplifiers?

Think he is refering to say Grey phase wire in rack 1 vs Black phase wire in rack 2. Only between those two wires will you see 400V, i think he is saying that they go to transformers and are stepped down after that.
Sounds a very small risk really, label away

 

[Knobhead]

How long has this system being in use? Anyone been fried yet?

I personally would not alter it. Label each rack as 400V not the amplifiers they are a self-contained 230V unit

 

[steveberry11]

Use these lables to indicate that there is 400V present between adjacent equipment

 

[Rockingit]

I understand your concerns about cross-phase faults, but I'm a bit confused as to why they've chosen to do this in the first place!

I worked as a sound technician for many years and we ALWAYS ran ALL the amps (on our systems, these sometimes drew in the region of 100A!) on the same phase (where I was, the blue phase, as it was at the time, was always for sound gear, the red and yellow were for the horrible lighting techies!)

15A per rack really is nothing, just a little more than a decent domestic kettle.

As I understand, to comply with the regs you just need to stick the 400V stickers on the racks.

Theatres having a 'clean' phase is more to do with having a separate earth than separstion of phases. Unless the place has a chuffing enormous 3ph isolating transformer in place, it's a bit of wasted exercise tbh. There's a thread on here [somewhere] about clean earthing. In a touring situation, most big amp racks in my experience these days are set for 3ph - almost all modern high power amps use switched mode and common rail power supplies internally and they don't really care what's going in so long as you get ------------ coming out!