Fire alarm shows fault when pub gets busy

Hi all I was hoping someone could help. The fire alarm in our pub seems to work fine and passed its testily test recently,  but sounds a fault when the pub gets busy. It shows a general fault and a small light shows an earth fault.  Would anyone know what could be causing this as it only happens when the place us busy?

possily a damaged cable. once everyone piles in, building moves slightly due to the weight (may only be a mm or so if that), fault appears. building empties and fault clears...

or could be a nail partially through a cable. again, bit movement enough to cause a fault but then clears. really, its going to need some fault finding by someone who knows what they are doing

Or could it be that certain other appliances, accessories are in use when the building is busy, inducing voltages onto the fire alarm system or affecting the power supply to the panel. But not in use when the pub is quiet? e.g. An overheating faulty cable joint on a circuit may cause strange symptoms. Do you have any high power kitchen type appliances on the go cooking pub meals that have greater usage when more customers pile in?

Doc H. 

Doc Hudson said:

Or could it be that certain other appliances, accessories are in use when the building is busy, inducing voltages onto the fire alarm system or affecting the power supply to the panel. But not in use when the pub is quiet? e.g. An overheating faulty cable joint on a circuit may cause strange symptoms. Do you have any high power kitchen type appliances on the go cooking pub meals that have greater usage when more customers pile in?

Doc H. 

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Thanks for the reply There are lots of things in the kitchen, but they are on whether  we are busy or not.

Doc Hudson said:

Or could it be that certain other appliances, accessories are in use when the building is busy, inducing voltages onto the fire alarm system or affecting the power supply to the panel. But not in use when the pub is quiet? e.g. An overheating faulty cable joint on a circuit may cause strange symptoms. Do you have any high power kitchen type appliances on the go cooking pub meals that have greater usage when more customers pile in?

Doc H. 

Click to expand...

Andy™ said:

possily a damaged cable. once everyone piles in, building moves slightly due to the weight (may only be a mm or so if that), fault appears. building empties and fault clears...

or could be a nail partially through a cable. again, bit movement enough to cause a fault but then clears. really, its going to need some fault finding by someone who knows what they are doing

Click to expand...

Ok thank you I did think it may be a loose wire, I will get someone in.

Is this a conventional or addressable fire panel?

Might be easier if , as UNG  asks,   its an addressable system .   

 You could try isolating a different  zone  each busy period   which may involve removing wires and inserting an EOL  device .   That could point you in the right direction , then you 'd have to investigate that zone . 

I'd love to know what the cause is .        Wonder if its as simple as a slightly dodgy heat detector reacting to the rise in temperature ,  a fire door jammed against a smash glass , or as Andy says ,  a cable fault made worse by the number of people somehow . :C   

Just a thought... How hot does your kitchen get at high level when the pub is really busy , particularly the extractor ducting , if you have any?

Excess heat and grease can do strange things.

UNG said:

Is this a conventional or addressable fire panel?

Click to expand...

Thanks - It's a conventional panel - Alarm sense Sigma CP-A  ka11040M2 If this helps

ruston said:

Just a thought... How hot does your kitchen get at high level when the pub is really busy , particularly the extractor ducting , if you have any?

Excess heat and grease can do strange things.

Click to expand...

The kitchen does get hot but, the bar gets busiest after the kitche  shuts at 9pm which is when the fault occurs.