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]

I'm a little confused about the function of the c/o switch. The UPS is usually responsible for the switching if the main supply fails. They usually react within a half cycle to keep servers running. If the c/o switch interrupts the power to the UPS for 0.5 seconds it will see this as power fail, 0.5 seconds is slow in the world of uninterrupted power.

You can use a potential free contact to operate software such as parachute via the serial port of USB interface.

 

[Engineer54]

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

1/ I don't understand the idea of having a 2ph and Neutral supply when your currently using a single phase supply to this load... But you will still need to have a means of protection and for isolating the C/O switch...

2/ You never leave a solid neutral at a C/O switch, the neutral must always be switched

3/ UPS systems switch over from one supply to another within half a cycle, far far quicker than th 0.5 sec your quoting. That's why they are called '' uninteruptable power supply'' lol!!

4/ Need to know far more about your system to answer that question. Those volt free contact can be for many uses!!

 

[Jonny66]

Hi Marvo,
Thanks for the reply.

The server room DB is currently supplied from a single phase of a three phase system. Over the last year or so the main supply has been lost on one of the phases a number of times usually affecting the server room and usually during the night. The DNO have been trying to solve this but to no avail at the moment. I suppose the clients idea is to use an auto c/o switch to try to over come a lost phase when nobody is o the premises.
Jon

 

[Jonny66]

Hi Engineer54,
thanks for the reply

1/ 2ph and N to try to avoid one of the phases going down which has happened several times, means of protection suppliers fuse and switch fuse at start of submain. Agreed isolation of c/o switch is needed.

2/ can I ask why? I can understand if a generator is involved, but if the c/o switch is switching from one phase to another, on the same mains intake and isolation is provided before C/O switch, would the neutral still have to be switched within the C/O switch?

3/4 - fair point
Jon

 

[Engineer54]

As Marvo stated, the UPS system should be doing the change over sensing and operation, via it's own change over switch facility. The generator control panel will doing all the sensing as far as the C/O switch is conserned and automatically start the generator on loss of prime power, and when prime power returns, will activate C/O switch to return to prime power supply. There's a bit more to it than that, but that's the basics if you like

The change over between mains supply and the generator supply to the UPS can be several seconds, it doesn't matter as the batteries will be taking up the load during the change over operation. Once the generator has started and up to speed and supplying a voltage that is acceptable, the generator controls will Switch the C/O to generator and providing the UPS is satisfied with the voltage stability, will internally switch from battery supply to generator/mains supply. Remember both the mains and generator supplies will be via the UPS system, and only isolated from each other by the change over switch...

 

[Marvo]

Ahh, it makes a bit more sense now, I was probably just being slow tonight. What sort of load figures are on the single phase supply to the servers (amps or KVA)? How long does the customer need to ensure there's back-up power in the case of main supply outage? Is it just to soft shut-down the servers or must the servers stay up during the entire power outage?

 

[Engineer54]

Sorry, .... didn't read your post correctly it's just a change over between 2 phases that your asking about. ...lol!!

 

[Jonny66]

Thank god for that LOL I was really confused then.

Yes its a change over between two of the phases.. so should the neutral still be switched?

 

[Spazz]

So to get this right you want to change over L1 with L2 of the 3 phase? or are you changing from 3 phase to single phase when you get a power shortage?

 

[needasparks]

Just about to say that. I assumed a gen-set also

 

[Engineer54]

As The neutral is derived from the same supply then i can't see a problem with the neutral being on a solid link. The change over in this set-up is obviously going to be a lot faster than if a generator was involved. You are however going to need to make one of these phases the ''prime power' and the other as Stand-by power'' so that the C/O switch normally runs in the prime power position.

What are you going to use to initiate change over, an under voltage relay in the prime power phase??

 

[Marvo]

The question also begs if one of the phases has some kind of latent fault and is prone to outages why not set up permanent camp on a more stable phase instead?

 

[Jonny66]

Marvo, I know I need some of the info above before going any further, but unfortunately I dont have it at moment, just been thinking about possible scenarios before survey installation etc. The sub main I believe is protected via 60-amp fuse switch, supplying 8way board with mostly 16 and 20 amp cbs.

As for time of backup power I would imagine as long as pos and worst case soft shut down. However, all I have been asked for is auto change over of phases, UPS to be source and installed by client.
thanks again.
Jon

 

[Knobhead]

Sounds weird to me but if they’re prepared to pay it’s fairly simple. Personally I’d be jumping up on down on the DNO.
Question 1, when one phase fails do the other’s remain OK, or do they fail randomly between each phase?
Question 2, what loading are we talking about?
Question 3, what other loading is on the back up phase, is this going to be switched over or off?

 

[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....

 

[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.

That sounds a bit on the expensive side for a single phase changeover switch to be honest!!!