Strip lights go out when I turn on the saw

[Nozzle]

Morning all,

I had my house extended recently, and I've only just got around to working in the new garage. I have discovered when I start my circular saw the strip lights go out! They come back on again afterwards but clearly something is not right. I didn't do any of the wiring myself, it was all done with a registered sparky and it is also all signed off. To add a bot of context though, it doesn't always do it so in persuit of getting more info, I used a consumer plug-in volt meter (the kind that also measures frequency, VA, power, p.f, and current) and can see the voltage is a little low (the sparky did mention this at the time). When it is down at 215 volt, starting the ciruclar saw causes lights to go out. When it is slightly higher, 220 or more, the lights will stay on.

I had confirmation from the missus who was sat in the original part of the house that none of the lights in there went out including florscent). I have noticed the lights do flicker a little at any time of day. Power to my house is provided by overhead cable. Is there anything I can do to get the voltage increased a little, or get put on another phase? What infomation/evidence should I ask my sparky to provide so I can get UK Power Networks to take this problem seriously? (I do have a video clip of lights going out while saw starts).

http://s825.photobucket.com/user/mininozzle/media/House stuff/LightsOut_zps561e3646.mp4.html

Nozzle

 

[DaftPunk]

What's the voltage like in your house?

Sounds more like the cable to your garage is too small rather than a network fault.

 

[plugwash]

Where are you plugging in the power meter? does the voltage reported by it change when you plug the saw in? Did the lights stay out for as long a the saw was turned on or come back on while the saw was still running?

It sounds like the voltage being delivered by the utility is on the low side but may or may not be actually going outside allowed tolerances within the allowed range and that the combination of volt drop on the feed to the garage when powering the saw and low voltage in the network caused the lights to fail. It's worth giving the supplier a call but you may not get anywhere.

You may also be able to solve the problem by changing the ballast. AIUI electronic ones are less sensitive to input voltage fluctuation than traditional ones. If you are using a circular saw you should really be using a high frequency electronic ballast anyway as using a conventional one can cause dangerous stroboscopic affects.

 

[PrenticeBoyofDerry]

Have you tested the distribution supply voltage in relationship the voltage supplied at the garage. Are we talking about a considerable distance between garage and the distribution board?
What details are on the certificate, cable size, MCB rating and out of interest what were the Zs readings?

You will have an inrush current when the circular saw starts up, this is likely to be effecting the performance of the light at this time, If you keep the saw running does the light then come back on?

 

[davelx]

You will have an inrush current when the circular saw starts up, this is likely to be effecting the performance of the light at this time, If you keep the saw running does the light then come back on?

He says that they do in the OP, I believe: "They come back on afterwards". I don't think he means after he turns the saw off.

 

[big-all]

a saw that size will only be around 1200-1500w
i wonder if theres any other load on at the same time ??

 

[Nozzle]

Good evening, thanks all for your responses.

As an aside, I popped into the garage earlier to take these readings and the lights were turning themselves on and off without the help of the saw! (Which has 1600W on the rating label, 1800VA when starting, down to 900W when running idle... I didn't dare look at the meter while running the saw loaded!).

The garage is 10-15metres away from the consumer unit, the meter is only a few meters further on than that. I snapped the plug-in meter showing as low as 193 volts, the only thing running in the garage at this time were the 5 strips lights and a radio running from a PC Power supply. I ran around the house and took more voltage measurements while the "minima" lasted, it was the same on old and new circuits. With the kettle plugged in and on, it went down to 179volts.

The data from the certificate for the extension ring main is: 2.5mm2 r1=0.9 ohm, rn=0.9ohm r2=1.53 ohm R1+R2=0.64. Smallest IR was 196MOhm Zs=0.86 ohm.

I get the impression the volts are poor across the entire house, but these lights are more sensitive to low voltage than anything else. I also have a ceiling fan that noticably changes tone when going slower and faster, plus the toaster, despite being good quality, doesn't glow that well.

Nozzle

 

[Iggifer]

what does your plug in meter tell you the volts are if you plug it in inside?

If it's accurately reporting 193v and it's not much different to the meter I would give the DNO a call. Or a spark with a calibrated test meter to come test it properly then call them

 

[Nozzle]

At that time when I rushed around the house (about 4:40 in the afternoon) they were all showing about the same. The garage is an integral part of the house, rather than something at the bottom of the garden on the end of a length of cable.

I'm hoping to get the sparky that did the work on-side to see if he can take some measurements with his calibrated meter. I only have the plug-in thing or a cheap DVM that doesn't 'do' RMS measurements.

Nozzle

 

[JohnW2]

I only have the plug-in thing or a cheap DVM that doesn't 'do' RMS measurements.

Do you mean that your DVM cannot measure AC voltage? If it can, the figures it displays will almost certainly be RMS ones.

Kind Regards, John

 

[westie101]

Or a spark with a calibrated test meter to come test it properly then call them

No need, ring the DNO tonight and report it as low volts their staff will attend and test it with a calibrated meter for no charge! They will also fit equipment to record the volts over a few days before doing the necessary to correct the situation.
Right or wrong volts (and they appear wrong) there is no charge for this service

Other than that, has the problem recently started or do you think it has been bad for some time?
Are you overhead or underground fed?
Rural or urban?

All of these could have a bearing on this problem

 

[plugwash]

Do you mean that your DVM cannot measure AC voltage? If it can, the figures it displays will almost certainly be RMS ones.

Or rather they will be some approximation of RMS.

The most "interesting" and therefore common measure of voltage on an AC system is RMS. However RMS is actually rather tricky to measure properly and accurately. So many multimeters mease something easier to measure (such as mean magnitude) and then scaled it to give an approximation of RMS.

AIUI "true rms" multimeters sample the signal at high speed and then calculate RMS digitally. This can have problems too though if you have signals that are very spiky.

Still probablly not something you need to worry about when measuring domestic mains. If it's significantly different from a sinewave you have other problems.

 

[Aragorn84]

One of the first digital multimeters i owned (perhaps 10-15 years ago?) had a note in the manual that when on AC mode it would display peak voltage, not RMS.

Sure enough when put across the mains, it would read around 350v.

 

[JohnW2]

Do you mean that your DVM cannot measure AC voltage? If it can, the figures it displays will almost certainly be RMS ones.

Or rather they will be some approximation of RMS. The most "interesting" and therefore common measure of voltage on an AC system is RMS. However RMS is actually rather tricky to measure properly and accurately. So many multimeters mease something easier to measure (such as mean magnitude) and then scaled it to give an approximation of RMS.

Indeed so - and in the era of analogue meters, there really was no practical alternative for run-of-the-mill meters. However, if the voltage being measured is a true sine wave, then the calculated RMS figure will approach the true RMS voltage, since the relationship between mean (or peak) and RMS is obviously fixed (and known) for such a waveform.

AIUI "true rms" multimeters sample the signal at high speed and then calculate RMS digitally.

True, but (although I may be wrong) I suspect that DMMs used by most people reading this post will not do that - just as with their analogue ancestors, they probably just calculate an RMS figuire on the assumption of a true sinusoidal waveform.

Still probablly not something you need to worry about when measuring domestic mains.

Exactly. The above is really much more academic than I intended. I was merely making the point that if the OP had a DMM which offered AC voltage measurement at all, it would almost certainly be (an approximation to) RMS voltage that it displayed - I don't think I've ever seen a meter which displays (or can display) anything other than RMS outside of an academic or industrial setting. [Edit: even though Aragorn clearly has! ]

Kind Regards, John

 

[JohnW2]

One of the first digital multimeters i owned (perhaps 10-15 years ago?) had a note in the manual that when on AC mode it would display peak voltage, not RMS. Sure enough when put across the mains, it would read around 350v.

Interesting, and a bit odd - since very few 'ordinary users' of a DMM would want peak voltage, and they would virtually all be measuring something which was close to sinusoidal (so that the conversion would be easy).

I bet that caused some confusion amongst users!

Kind Regards, John