FAS fed from temporary generator!

[Benzerari]

A fire alarm system reporting 'AC fail' fault, for several times during the day, it's fed from a temporary generator due to power cut for days..., the voltage test shows non stable supply voltage, some times it goes till 295Vac, and some times it drops down to few volts...,

Questions:

1- Who's responsibility to have a stable power feeding the fire alarm system 24/7?
2- Would this instability in voltage and current affect negatively the batteries..., (reducing their life cycle)?
3- There is unusual heat inside the fire alarm panel; would that be due to increase in power supply, from time to time?
4- The generator is feeding the whole site, would that be a must to have a separate generator to feed the fire alarm system only?

Thank you Guys

[Allen Higginson]

A fire alarm system reporting 'AC fail' fault, for several times during the day, it's fed from a temporary generator due to power cut for days..., the voltage test shows non stable supply voltage, some times it goes till 295Vac, and some times it drops down to few volts...,

Questions:

1- Who's responsibility to have a stable power feeding the fire alarm system 24/7?
The client,in the same way as in the case of a new install it is the customers responsibility
2- Would this instability in voltage and current affect negatively the batteries..., (reducing their life cycle)?
More than likely that they'll end up cooked
3- There is unusual heat inside the fire alarm panel; would that be due to increase in power supply, from time to time?
Yes and will probably end up goosing the panel
4- The generator is feeding the whole site, would that be a must to have a separate generator to feed the fire alarm system only?
They are going to need some sort of stable power supply and not only for the fire alarm system either by the sounds of things!
Thank you Guys

[kurnal]

Benz thats some overvoltage and the responsible person should consider its effect on other equipment in the building too. Presumably the 295 volts is only  happening off load?

[John Webb]

I had a similar problem recently at my local church's Parish Centre. There had been a power cut for a short while and when I went to check on things the church, fed off one phase, was fine. The other phase feeding the Centre was all over the place with the voltage fluctuating between 190 to 260 volts - not quite as bad as Benz's. But the emergency lighting kept coming on and going off, as did the FA panel's Mains supply indicator and fault alarm. I found out that the phase concerned was being supplied by a network-provided generator following a high-voltage cable fault nearby.

I too was concerned about surges and things. Fortunately there was no-one in the centre, or due in, and in the end I turned off the whole supply and left it off until the mains was restored to stability the following day. Did give an opportunity to check out the emergency light batteries a couple of months in advance of their usual check.....

But short of interposing a UPS between the mains and the FA panel I cannot suggest any easy remedy for this one.

[Wiz]

Many fire alarm control panels have monitoring of the mains supply and will give a fault condition if the supply varies approx 10% above or below the norm. This fault warning is provided to advise of a problem that is potentially damaging.

Years ago I was told that the electrical distribution companies have agreed to supply electricity within 6% of the stated voltage. I don't know how true this is, but there must be some figure that control panel manufacturers work too in their design of it's electronic circuitry.

It is obvious that if a transformer output gives out say 24V for an input of 230V then if 296V is applied to the transformer input then the output will be in the region of 29V. This voltage may be too high for the circuits that regulate the panel supply voltage and the battery charging circuit.

I would imagine the battery charging circuit in modern control panels would have voltage regulation to maintain the correct battery charging voltage at a high input voltage so the batteries are unlikely to 'cook'.  But if this voltage regulation circuit can't handle 29V input then it will fail at some time and the batteries probably won't charge at all.

If the fire alarm system is not modern and uses old-fashioned battery charging circuity (i.e not current BS) then it would be quite likely that a high mains supply voltage would have the effect of providing a high secondary voltage that may cause damage by overcharging the batteries.

[Benzerari]

Benz thats some overvoltage and the responsible person should consider its effect on other equipment in the building too. Presumably the 295 volts is only  happening off load?

Yes certainly; I just wonder that generators will probably never replace the mains supply for the simple reason that generators are not highly engineered to supply a stable feed, regardless of the loads variations, particularly when the load is a mixture of a lot of electronics equipments not just lights and normal appliances such as, washing machine, fridge, TV..., when it comes to high tech equipments around, which they normally need a very good stable supply the generator becomes a nightmare or at least the worst solution if not part of anticipated problems.

[Benzerari]

I had a similar problem recently at my local church's Parish Centre. There had been a power cut for a short while and when I went to check on things the church, fed off one phase, was fine. The other phase feeding the Centre was all over the place with the voltage fluctuating between 190 to 260 volts - not quite as bad as Benz's. But the emergency lighting kept coming on and going off, as did the FA panel's Mains supply indicator and fault alarm. I found out that the phase concerned was being supplied by a network-provided generator following a high-voltage cable fault nearby.

I too was concerned about surges and things. Fortunately there was no-one in the centre, or due in, and in the end I turned off the whole supply and left it off until the mains was restored to stability the following day. Did give an opportunity to check out the emergency light batteries a couple of months in advance of their usual check.....

But short of interposing a UPS between the mains and the FA panel I cannot suggest any easy remedy for this one.

What about the solution of a separate generator to feed the  FAS as; the FAS will be its unique load?

But the idea of the UPS is great, why UPS is recommended for other computers and electronics equipements and not for fire alarm systems?

[John Webb]

The batteries in an FA panel in effect constitute a UPS, just that we don't bother using the batteries to power an inverter to give a stable mains voltage, since the FA components happly work at the low voltage and thus cut out the cost of an inverter. Installation and maintenance is also simplified by the circuits being of SELV (separated extra-low voltage) type.

Main concern to me would be the potential for damage to the charging circuit with such a large variation of input voltage, which may also include nasty spikes as well which would only be revealed by more sophisticated instruments than the usual volt-meter.

[Benzerari]

The batteries in an FA panel in effect constitute a UPS, just that we don't bother using the batteries to power an inverter to give a stable mains voltage, since the FA components happly work at the low voltage and thus cut out the cost of an inverter. Installation and maintenance is also simplified by the circuits being of SELV (separated extra-low voltage) type.

Main concern to me would be the potential for damage to the charging circuit with such a large variation of input voltage, which may also include nasty spikes as well which would only be revealed by more sophisticated instruments than the usual volt-meter.

The inverter is certainly part of the UPS to give 230Vac, but the other important thing of the UPS is that, it gives a stand by stable feed for at least 1/2 hour or so depending of the makes, in case of power failure, regardless of the fluctuations of the mains source..., still the main issue is why NOT BOTHERING about having a proper UPS for fire alarm systems, cutting the cost is less safe in this issue isn't?

The traditional standby batteries are normally in charge of feeding the system in case of power failure but the UPS may add further safety even with that instability of the feed generated from a temporary generator. The added safety is not only for keeping the system fed for longer time, but also for preventing equipment damage from that high fluctuation...

[John Webb]

Sorry, I wasn't clear if you were proposing the use of a UPS just for this particular case or in general, and perhaps responded thinking you meant the latter case.

A UPS in the present circumstances is quite sensible if the problem is to go on for some time and if the UPS can cope with the wild swings in voltages.