Auto Change Over Switch Advice

[Jonny66]

Hi,

Need some advice regarding the installation of an automatic change-over switch to protect the supply to a small commercial server room with two cabinets.

The building has a three-phase TNS supply, and at present, the sub main supplying server room DB is a single phase 3 core SWA (L/N/CPC) protected by a single phase fused switch at mains intake.

To protect the server room supply the client has suggested that an automatic C/O switch be installed, in conjunction with a UPS system that the client will arrange. I have been asked to source and install an auto C/O switch utilizing two phases, but have never installed one of these. So before I agree to price and take this on thought it would be wise to ask you knowledgeable people, your views on the following.

1. Mounting an auto C/O switch at the mains intake, upstream of the single phase switch fuse, i.e Henley L1, L2 , N (and CPC from MET) and take these tails (<3m) into C/O switch - then take single phase & N (& CPC) from load side of C/O switch into a fused switch and use the existing <8m long sub-main to server room DB .

2. Having never wired one of these (will discuss with manufacturer) but was wondering - as the neutral would not need to be switched with the phases should I be sourcing a two pole C/O switch (two phases switched) and N in solid link . To be honest I would like to know what was the general set up inside one of these, regarding terminals etc…?

3. Have read that the auto change over of phases can be quick at around 0.5 sec and as such, would this change over speed bring in the UPS?

4. Finally, have also read that voltage free contacts can be installed into auto C/O switch and are used to send a signal to a UPS system, could someone explain whether these are always needed.

Hope this makes some sort of sense
Thanks in advance
Jon

 

[Marvo]

No probs, I thought you had a finalized plan. You can do what you're suggesting but it could get complicated and somewhat messy. You might consider a system where the c/o switch gives the option of switching to any one of all three phases rather than just two and it's powered by the UPS.

It's just very unusual where only one phase of a 3-phase system is unstable. I can't help thinking you might be better focusing further efforts on remedying the actual root cause in conjunction with the DNO rather than spending a fortune on workaround that will provide possibly only limited relief.

 

[Jonny66]

Nicholas Owen, change from L1 to L2 in the event of L1 going down.

Engineer54, thanks, thats what I thought regarding N. Yes I understand that one of the phases will be the prime power and other as back up. As for the c/o switch I would purchase that from a manufacturer.
Marvo, the more I think about it now, I think you might be right "set up on more stable phase". I think the problem is that the client believes having two phases is better than one.

 

[Spazz]

The UPS will stop the servers being shut down - thats their job.
The Auto Switch will switch over, with the UPS taking up the slack


As far as the nutrual I cant answer because I dont know enough about 3-phase.

It would be worth mentioning to the clients about swapping to a more stable phase, as that may only need swapping 1 wire over (again I dont know the setup)
Saving money and time.


Just thinking out load about a potential problem Im not sure of:
Taking L1 as primary phase and L2 as backup
once L1 has been restored, thinking an auto change over is a relay, would there be a potential for a 'spark over' between L1 and L2 as the relay clicks back to L1 supply?

Again I dont know enough about 3 phase so this is a learning curve for me - I know they are both live, but with the sine wave offset from each other (as a delay)

 

[Engineer54]

What also needs to be considered, is what happens in a general power cut?? The UPS needs enough time to allow an organised shut down. Generally a UPS powered between a mains and generator source will have a a capacity to run at a designated load of between 10 mins and 30 mins. Your system needs to be able to provide a warning to operatives to safely shut down computer system, at such times as in power cuts or C/O switch failures...

 

[Knobhead]

A decent UPS will have the facility to shut the system down if there’s a danger of failure. But it all adds to the cost.

 

[Engineer54]

A decent UPS will have the facility to shut the system down if there’s a danger of failure. But it all adds to the cost.

Yes, that's what i'm used too as well, but it still takes time for that program to do it's business...
ie saving data that's not been stored etc...

 

[Jonny66]

Tony,

1, Good question and one I have been asking them. Their answer is that the server usually goes down, however not always. The building is quite old and the circuit details are not what they should be so I think this is something that needs sorting.
2, Quite low I think but again I havent survey the site yet
3, switched over and I would imagine the existing load on the backup to be quite small, two story office in old Victorian building.
Think they've given up on DNO at moment, although I saw a UK Power network van parked on side of the road just up the street when I was there the other day. I could smell the tea and biscuits

Marvo
another good option c/o switch utilizing all 3 phases.

thanks guys loads to think about

 

[Engineer54]

another good option c/o switch utilizing all 3 phases.

That could get complicated, and expensive to put into operation ...lol!!

 

[Knobhead]

another good option c/o switch utilizing all 3 phases.

That could get complicated, and expensive to put into operation ...lol!!

Sounds an interesting chalenge :drool5:

 

[Engineer54]

2. Having never wired one of these (will discuss with manufacturer) but was wondering - as the neutral would not need to be switched with the phases should I be sourcing a two pole C/O switch (two phases switched) and N in solid link . To be honest I would like to know what was the general set up inside one of these, regarding terminals etc…?

Just read this paragraph again, ....You will NOT be switching two phases you will only be switching Phase and neutral!! If you imagine a 3 position switch two incomers and a load or outgoing. you will be switching only the incomers to the load ...ie L1+N to Load or L2+N to load. not L1 and L2 to load.

Are you intending to use a motorised switch or contactors?? Personally, i don't like using contactors as they need to be mechanically interlocked as well as electrically interlocked whereas a switch is only electrically interlocked via the motorisation....

 

[Jonny66]

Engineer54
That could get complicated, and expensive to put into operation ...lol!!

Ok fairly expensive, I believe an auto c/o is around £650 then isolator and tails needed. the submain and fused switch are already there. Why will it be complicated am I missing something again.

 

[Jonny66]

Engineer54

Just read this paragraph again, ....You will NOT be switching two phases you will only be switching Phase and neutral!! If you imagine a 3 position switch two incomers and a load or outgoing. you will be switching only the incomers to the load ...ie L1+N to Load or L2+N to load. not L1 and L2 to load.
Thanks

Again, I would not try to build one of these I would purchase one from someone like Macklin.

 

[Jonny66]

Engineering54
What would you suggest in this instance. I know ideally the DNO should fix the problem and they probably will eventually, but the client is paranoid about losing the phase on the server. They are going to invest in new UPS systems but they also would like the option of two phases. Im starting to doubt whether this is a good option.

 

[Engineer54]

Engineer54
That could get complicated, and expensive to put into operation ...lol!!

Ok fairly expensive, I believe an auto c/o is around £650 then isolator and tails needed. the submain and fused switch are already there. Why will it be complicated am I missing something again.

Think about it, a single phase UPS being supplied from any of the 3 available phases, it'll be like a flip over arrangement!! lol!!

 

[Engineer54]

Engineering54
What would you suggest in this instance. I know ideally the DNO should fix the problem and they probably will eventually, but the client is paranoid about losing the phase on the server. They are going to invest in new UPS systems but they also would like the option of two phases. Im starting to doubt whether this is a good option.

Nothing fundamentally wrong with the idea, never seen it before mind!! Generally you tend to loose all 3 phases rather than just one. Different if the supply came from 2 separate sources...lol!! From what your saying, there is a tendency for one of these phases to go down, but no-one seems to know the reason, or has bothered to investigate further... Does anyone know for sure that it's a DNO problem, and not an in house problem??

So as a make shift remedy, they are skirting around the problem, so complete lunacy to incorporate this phase into what is going to be a maintained service. So, if the problem is on L1, use L2 and L3....