power surge

[degs]

Would it be possible to damage components in underfloor heating wiring centre with power surge .if so how can you determine if a power surge is causing the problem also lamps make a loud pop when blowing ?

 

[steve-aka-g]

yes you can damage the underfloor heating controller with a power surge, get a qualified spark in to test it and if it is the case put a power surge protection in.

 

[Marvo]

'Power surge' is one of those blanket/cover-all explanations that people often come out with when they've no idea what actually caused the problem. It conjures up a magnificent picture in the head of people that know very little about electrical networks of a tsunami of electricity wreaking havoc wherever it goes and hitting the poor appliance which obviously stands no chance.

I would never let anyone use the term 'damaged by power surge' and get away with it unless they could convince me they'd ruled all the other possible causes out of the equation by thoroughly testing the circuit and its origin. Even then I'd be highly skeptical and would check the control board to see what components had suffered damage.

As Steve suggests get the circuit and the CU inspected and tested, there'sa very good chance this type of damage could be cause by a poor termination or other common problems.

 

[degs]

Thanks for your advice appreciated

 

[sparc]

Had an instance today - out of my experience to date - which 'suggested' damage from some sort of 'transient power event' though - having read Marvo's comments I'm not going to mention 'surge' or 'spike' here.

There had been some power outages in a small area - limited number of homes affected, and DNO had attended to sort of problem. Afterwards one customer had a number of appliances dead - all appeared to be ones with electronics in them - such as video amp, microwave etc. Other equipment - ovens, PCs, fridge (with digital displays), TVs, etc, are okay.

No RCDs or MCBs tripped, no plug top or FCU fuses blown.

My initial thought was something external had caused the problem, but found out that no of the neighbours had any damage done.

I then read in a Siemens brochure that most electrical transients are caused by other equipment in the home - particularly equipment with large motors. This property has a large air source system.

DNO is having none of it - nothing on their side could have killed all the appliances.

As this was a quick call out I haven't yet had time to do an analysis of what's on which circuits - there are three FULL CU's in the property - priority was to restore power to heating systems, which I did by replacing the stone dead controller.

Has anyone any experience of internal equipment causing a transient that could cause so much damage? Marvo mentions loose connections in a CU - could that do it?

 

[i=p/u]

A friend of mine back home was at hotel replacing everything electronic as was fryed which was caused by the neutral loose/burnt

 

[sparc]

Wow! I took a look at board and couldn't see anything obviously amiss, but will check again first thing in morning! Thanks for that.

(Although it seems a coincidence that this happened the day the DNO were working on pole outside!)

 

[Lucien Nunes]

An expert can glean useful info from studying the dead appliances. A true transient will be a very short impulse of a high voltage. High energy transients will vapourise PCB tracks, weld contacts, shatter LBC fuses and VDRS etc. Lesser transients will cause semiconductor failure and possibly less destructive fuse failure when VDRs conduct. Neutral loss will cause only 400V max overvoltage, often less, for a much longer period. Common signs are burst electrolytics, tripped thermal cutouts and non-vapourising fuse rupture.

As Marvo says a 'surge' is a catch all term that most of us have used as a get-out-of-jail for 'your equipment broke but we don't know why yet'. I had a major equipment failure during a show once for which people were demanding answers before I could even start the post mortem - I kept them quiet with a suggestion that it might have been a surge from an aircon compressor and nobody ever questioned it, they all thought that was a very good reason as it could be blamed on someone else! Of course, surges do happen.

 

[micknew]

Earlier this year we were called to a garage because the fluorescent lights were varying in brightness.
Also computer equipment had failed.
We traced the fault to a loose screw on the neutral block in the main switch feeding the distribution switchgear.
The installation had been tested a week before and the sparks had not tightned the neutral screw when he finished testing.
The result was 285V L-N.

 

[sparc]

Must confess I don't understand science behind this higher voltage on a loose connection ... If the supply voltage is 230V how does it get to 285V - assuming there isn't actual an air gap?

Still a mystery with my job - I'd gone back to check neutrals and they all were solid. Checked RCD, that tripped the numbers nicely.

 

[i=p/u]

Even try dno connections ....

Maybe be spu devices are the way forward

 

[Lucien Nunes]

this higher voltage on a loose connection ... If the supply voltage is 230V how does it get to 285V

This relates specifically to a faulty neutral in a three phase system with unbalanced loads. Take the simple example of a three phase DB with three single phase finals, one on each phase. One is loaded with 1kW resistive load, one with 3kW and one unloaded. Normally, all three circuits see 230V line-neutral because the neutral is defined by the supply transformer and carries the necessary out-of-balance current arising from the unequal loading. If the supply neutral fails open-circuit, the two loads are then left connected in series via the DB's neutral bar, between the two lines 400V apart. Because the loads are unequal, the voltage divides unequally; the circuit with 3kW sees 100V and the circuit with 1kW sees 300V, totalling the 400V line-line voltage.

If there are many loads or a fair amount of balanced load, a high-resistance neutral connection will only cause the downstream neutral to 'wander' by a small voltage and the problem might last for some time before things start to go pop!

 

[micknew]

Must confess I don't understand science behind this higher voltage on a loose connection ... If the supply voltage is 230V how does it get to 285V - assuming there isn't actual an air gap?

Still a mystery with my job - I'd gone back to check neutrals and they all were solid. Checked RCD, that tripped the numbers nicely.

If the supply in the property is single phase then the lost neutral problem would only occur if the neutral was lost on the network side.