3 phase power

[Deleted member 121002]

If you are using a double conversion UPS i.e. ac to dc to ac
The voltage between any outgoing cable of 1 UPS could be 400v different from an outgoing cable of a second UPS
As a general rule, neither UPS will sync it’s outgoing frequency to either incoming mains or a secondary UPS
Therefore, frequency difference (very small) will likely shift the phase angle between the 2 UPS units outputs.

There are some special circumstances where the above will not apply.

All UPS systems (used in broadcast) are linked together (control wise) so that the Red, Yellow and Blue phases between UPS's remain in sync. You are correct that the outgoing phase maybe be different (not much) from the incoming because of the conversion from ac to dc and back to ac. But when connecting the outputs of each UPS to a dual mains MDU (mains distribution unit) the phases must be in sync, because the MDU's will switch at the zero crossing of the current cycle to minimise spikes and surges. The use of dual mains i/p MDU's are used mainly for euipment that have only have a single PSU.

 

[Deleted member 105166]

But since the equipment has 2x power supplies fed via IEC connectors. Both PSU's must be fed from different UPS's but on the same phase. In our case it could be very easy to get this wrong and have 2 different phases in the same piece of equipment...

The two power supplies are themselves different pieces of equipment, albeit in a shared enclosure. I don't see the issue.

 

[Deleted member 121002]

The two power supplies are themselves different pieces of equipment, albeit in a shared enclosure. I don't see the issue.

Hello, This is to provide a safe working enviroment. We dont need the possibility of 400v across two PSU's running on different phases, why take the risk? It is the preferred practice within Broadcast systems to have dual supplies within a piece of kit to be fed from two UPS systems (main and back up ) BUT on the same phase.

 

[Deleted member 121002]

Also if these two UPS feeds also provide power to a dual mains MDU, (please see previous posts regarding dual mains MDU's feeding equipment running on a single supply) In this case it is imperative to make sure the two UPS phases are the same.

 

[James]

Is this a documented or recommend practice,

Or

A we have always done it that way practice?

P.s not trying to be argumentative but I am struggling to see the reasoning behind it.

 

[Deleted member 105166]

Hello, This is to provide a safe working enviroment. We dont need the possibility of 400v across two PSU's running on different phases, why take the risk? It is the preferred practice within Broadcast systems to have dual supplies within a piece of kit to be fed from two UPS systems (main and back up ) BUT on the same phase.

You've got 400V between phases going on in loads of other OB kit, that in reality people are more likely to open up for whatever reason, such as dimmer packs, distro, etc.

 

[davesparks]

Hello, This is to provide a safe working enviroment. We dont need the possibility of 400v across two PSU's running on different phases, why take the risk?

What exactly is the risk? Just stating that there is 400V isn't describing the risk, just making a statement.
What scenario do you see occurring where someone will be exposed to this 400V?

 

[Deleted member 105166]

Also if these two UPS feeds also provide power to a dual mains MDU, (please see previous posts regarding dual mains MDU's feeding equipment running on a single supply) In this case it is imperative to make sure the two UPS phases are the same.

Can you provide a photo of one of these "dual mains MDU" units. I hope this isn't the posh title for a widowmaker. I'm particularly interested in the supply ends of the dual feed arrangements when one feed only is energised and the other disconnected.

 

[davesparks]

Is this a documented or recommend practice,

Or

A we have always done it that way practice?

P.s not trying to be argumentative but I am struggling to see the reasoning behind it.

In the entertainment industry as a whole, and especially theatres, there is an obsession with 'phase seperation' or keeping the phases at least 2 metres apart.
This is a hangup from many many years ago when it is required by the regulations and people just wont let go of the idea.

From talking to some people in the industry you would think that 400V magically jumps out of the sockets and grabs anyone walking past if there's 2 phases within a mile of each other.

 

[Deleted member 121002]

Can you provide a photo of one of these "dual mains MDU" units. I hope this isn't the posh title for a widowmaker. I'm particularly interested in the supply ends of the dual feed arrangements when one feed only is energised and the other disconnected.

Yes, I can provide details for you, look at this website ( I cannot post a web address), so.....look for tslproducts dot com , then find power management followed by automatic change overs. "MDU14-CO" I hope this helps, if you need more information or even photos of actual installations and I will be very happy to provide something for you.

 

[Deleted member 121002]

In the entertainment industry as a whole, and especially theatres, there is an obsession with 'phase seperation' or keeping the phases at least 2 metres apart.
This is a hangup from many many years ago when it is required by the regulations and people just wont let go of the idea.

From talking to some people in the industry you would think that 400V magically jumps out of the sockets and grabs anyone walking past if there's 2 phases within a mile of each other.

Yes, this hang up is alive and well....
As long as proper precautions are taken and there is proper labels and idents used I have no problem in having different phases near to each other. The view that you have shared has only very recently been removed and cables in racks within easy reach, its all ok as long as people follow good practices when installing stuff and do not cross phases.

 

[Spoon]

Here is the link @Omnibod mentions above.

 

[Deleted member 105166]

Yes, I can provide details for you, look at this website ( I cannot post a web address), so.....look for tslproducts dot com , then find power management followed by automatic change overs. "MDU14-CO" I hope this helps, if you need more information or even photos of actual installations and I will be very happy to provide something for you.

I've not read the spec in detail, but that looks like a proper piece of kit, designed to the relevant EN standard and incorporating a two pole 'break then make' changeover switch... therefore I'm unsure why the two supplies need to be on the same phase.

 

[Deleted member 121002]

What exactly is the risk? Just stating that there is 400V isn't describing the risk, just making a statement.
What scenario do you see occurring where someone will be exposed to this 400V?

The risk is minimal, anyone who takes the lid of kit whilst 2x different phases is live is asking for trouble. The scenario could (not would) be if equipment power shares using 2x independent PSU's running from different phases. Even in this condition using switch mode psu's the effect is unlikely to cause a problem. But why take the risk, minimal as it maybe. In Broadcast and related systems (editing, post production houses etc) often other non engineering types have access to power connectivity (when they shouldn't) and this is where problems could arise. Maybe it is considered to be overkill and you could be right, but ( I use this word a lot) we take safety very seriously and make sure there is no likelihood of having mixed phases no matter that the problems of doing so is minimal, i say again, why take the risk when we dont need too.

 

[Spoon]

Ok, so going back to your original post, the answer is: There is nothing in the regs to say that this supply is incorrect.
If you wish to go beyond the regs then that it up to you.
How about training people not to mess with things they shouldn't mess with??