Changover switch to mains fail relay rewire

[Tate]

I have to rewire in a mains fail relay that will inform us when REC power has been restored.

At the moment we have REC supply leading to changeover siwtch that is fed by the REC or a generator. The mains fail relay is upstream of this, so will indicate mains on either REC or generator.

I would like to wire the MFR so it informs us when REC supply is back only. This would involve connecting a 2.5-4mm single between the incoming side of the changover switch to an MCB that would inturn feed the MFR.

Are there any regs that say this is a no no?

Cheers

 

[DurhamSparky]

cant see any problem as long as you ensure you don't back feed the network with juice in ANY circumstances fault/mishap...!

 

[Engineer54]

I have to rewire in a mains fail relay that will inform us when REC power has been restored.

At the moment we have REC supply leading to changeover siwtch that is fed by the REC or a generator. The mains fail relay is upstream of this, so will indicate mains on either REC or generator.

I would like to wire the MFR so it informs us when REC supply is back only. This would involve connecting a 2.5-4mm single between the incoming side of the changover switch to an MCB that would inturn feed the MFR.

Are there any regs that say this is a no no?

Cheers

How does this relay sense generator failure if positioned upstream on the prime power side of things?? Once the generator is supplying the load, there should be no connection to the MFR, if you have , it means your MFR is connected wrongly at the changeover switch. It needs to be on the prime power mains side of the switch only....NOT on the load connections!! So if you only want to monitor the mains failure, all you need to do is change the MFR connection points at the changeover switch. Or am i missing something here?? Is this an automatic changeover switch or manual??

 

[Tate]

A bit more info required I think. The
system was designed with "cost" in mind
and therfore has no automatic components.

The MFR is currently fed via an MCB in the
distribution board which is in turn fed via
either REC or generator hence the MFR senses
mains from whichever source supplied.

The mains is monitored via GSM/GPRS telemetry
which will tell us when we loose REC mains.

The idea of the upgrade is to find out when
REC power is restored so the generator can
be left running and only attended when it
has to be refuelled or to manually switch
back to REC mains.

Thanks

 

[Lighthouse Phil]

Tate, why not just have a MFR on the supply side of your mains and not on the load side which it sounds like you have at the moment... Mains failure / supply is usually monitored from the Gen Set control cabinet....for auto starts / shut downs
out of interest..What is the gen suppling ?

 

[Engineer54]

You've totally baffled me now!! Why on earth would you intend to leave the generator running when mains power is restored??

Do you understand, that generators cost far more to run than the cost of mains power?? And that's without taking any maintenance requirements and renewables into consideration...

 

[Lighthouse Phil]

A bit more info required I think. The
system was designed with "cost" in mind
and therfore has no automatic components.


.
I think it'll cost more to run your genset then your going to save...Like E54 has said,, Do you reliase how much in the long run it'll cost to run a gen set...and with the ever rising price of diesel...hmmmm

 

[Engineer54]

A bit more info required I think. The
system was designed with "cost" in mind
and therfore has no automatic components.


.
I think it'll cost more to run your gen-set then your going to save...Like E54 has said,, Do you reliase how much in the long run it'll cost to run a gen set...and with the ever rising price of diesel...hmmmm

Exactly, designed with cost in mind so no Auto changeover, ....Then state that you leave the genset running when prime power is available!!! Someone at your place has lost the plot somewhere along the line. the auto changeover switch would have paid for it's self many times over if this procedure is the way you go about things ....lol!!!

 

[Knobhead]

I’m totally confused by this set up. Talk about spending a pound to save a penny!

 

[Tate]

Gents you are preaching to the converted, I told the designers the severe limitations to this system when we first installed it but, but hey, Im just the idiot who has to deal with it:wacko:

The system is for a series of cabins in the Highlands that runs a PMR system for winter awareness instructors to contact each other in the event of mobile phone failure.

 

[Engineer54]

Another thing you ought to tell your designers of this cocked up system is, Stand-by generators are not rated and not recommended for prolonged usage. Most will be rated for not more than 12hrs. So i strongly suggest that you advise them to go with an auto changeover switch, it will save a pot load of money in the medium to long term life of this Genny set-up!! What's the rating of this Genny (KVA) and what sort of load is it carrying during operation, is it a single or triple phase unit??

By the way, what's a PMR system when it's at home?? lol!!

 

[DPG]

PMR=Private Mobile Radio. Daz

 

[Engineer54]

PMR=Private Mobile Radio. Daz

Thanks for that!! You learn something new every day!! lol!!

 

[Knobhead]

I know this sounds expensive. But a UPS with a generator back up would be the cheapest option in the long run. As E54 has said a stand by generator is not designed for continuous running. When push comes to shove when the stand by is needed it’s likely to fail. Been there, got the tee shirt*. The cost of running a stand by 24/7/365 must be horrendous!

*As part of my duties as the newbie on a plant I ran the stand by gen sets up every week on no load. The one time we needed them they failed to take up the load! As the newbie I didn’t know they had never been used in anger until we needed them. I was a bit vocal about my thoughts on the “back up” system. But it was funny hearing 2 Rolls Royce V12’s spluttering.

 

[Tate]

Maybe I should have named this thread "The company that uses me to do works for them do cheap, crappy designs, however I'm not caring because I can charge them a fortune to take a generator to their site when the mains goes off"

The design is crap, I know. Can we get back on topic please.

I believe I'm covered by the 3m rule in Section 4.3.5 (or something like that) of the regs but I was wanting clarification before I burn down the installation.