Audio/Video equipment on same phase?

[Senselessticker]

A client has requested that some audio/video equipment (a few digital projectors, smartboards, etc..) be powered by the same phase from the same panel. Can anyone explain the advantage of doing so? The idea seems arbitrary to me.

Thanks for any help.

 

[dpc]

I see no advantage from an electrical viewpoint,and maybe some disadvantages. All of these devices have an ac/dc power supply, so incoming phase relationships are meaningless.

 

[alehman]

I had a CCTV supplier tell me that a few years ago. I think he claimed it would cause interference on the displays if the cameras were on a different phase than the monitor.

 

[IRstuff]

Not so much the phase relationship, per se, but there's always some possibility that the phase difference manifests itself as a ground potential difference in the low voltage circuitry, particularly if the low voltage ground is somehow tied to the AC neutral.

I don't know about your specific combination, but I've had different logic circuits interconnected with differential transceivers and being supplied from different DC supplies run from different AC mains. On power-on, the difference in AC phasing wound up coupled into the digital grounds and the net potential difference was equalized through the transceivers. They lasted on average about 3 power on/off cycles before the emitter juntions in the receiver inputs died.

If the equipment are intercoonected, they'll need to have a continuous ground connection between them to prevent any untoward behavior.

TTFN

 

[mc5w]

Most of the gasoline dispenser manufacturers such as Gilbarco require that the dispensers all be on the same phase as the control power for the pump controllers. However, that is only a safeguard against somebody who is testing the relays that send signals from the dispensers to the controllers by using a jumper wire. If he sticks a jumper wire in the wrong place he will create a power cross if the circuits are on different phases. The ways that I safeguard against that is to use 24 volts control circuits for the pump controllers and to RTV the coil terminals of the relay sockets to keep jumper wires and voltmeter probes OUT!

Also, if you are twinning 2 furnaces with electronic control boards for a 2 stage heating/cooling system the boards will screw up if they are on different phases of a 120Y208 volt power system. For some reason the phase difference messes up the electronics. What you have to do in this case is to wire both door interlocks in series and then power a 75 va control transformer and wire the boards to use only that control transformer for their 24 volt supply. You then have to use double pole power relays to power the blowers, 1 relay for each blower speed. You can still use the old control transformers to power humidifiers and fresh air dampers.

Also, a now outlawed 3-way switching circuit for knob and tube wiring is sometimes wired with a hot and neutral from 1 branch circuit feeding 1 switch and a hot and neutral from another branch circuit feeding the other switch. If the 2 branch circuits are on different phases 1 of the switch positions will put 240 volts of 208 volts across a 120 volt bulb. This is also how turning off 1 breaker or fuse does not totally disconnect the power - some things are not as off as advertised!

Those are the only 3 instances I know where putting 2 devices on the same phase does something useful.

 

[Prospero]

Supply quality
Maybe quality of the power supply and harmonics are an issue here too . . . With audio/visual equipment there is the possibility that any dirt on the power supply can get through and affect the system. On a digital system a power spike could concievably cause erratic behaviour or lock ups. If the equipment is on more than one phase there is a greater chance that this might happen.

Unbalanced phases
A counter to putting it all on one phase, is if the total load is enough you will unbalance the 3 phase supply and this could cuase larger neutral currents, and as your earth is connected to your neutral at some point in the system, you will get ground currents, sensitive equipment like audio/visual equipment don't like ground currents. Having said all that, I think this point is largely academic.

Dangerous voltages
As a policy in England, with domestic equipment you always put things on the same phase to minimise the potential shock voltage in the event of a mishap. IFor example If I am a service engineer and I stick my head in some dark and awkward cabinet to fix something I will be less pleased to find a 3 phase voltage floating under my nose than a single phase voltage!