Strange Problem

[Constant Electrics]

Hi, I am living in a country that has 220/240v ac supply. I am an electrician (UK trained) and just rewired a house . I have a weird problem. When I turn the electric shower on the fridge(on a separate circuit) Starts working overtime and makes a kind of loud 'compressor working overtime' hum. The supply to the whole house was only 10amps! (normal out here) and the shower is 3kw the fridge around 120watts max. 70 watts normal op. I upgraded to 20amps from the power company thinking that it was a power drain that was affecting the fridge as the 10 amp breaker kept tripping when the shower was used at 3kw (of course)  but the problem still occurs. Any ideas of resolving the problem? The fridge seems to be working normally ( no strange noises) when the shower is not running. Oh just another point- when the shower is on the 2kw setting the noise is much louder than when it is on the 3kw setting. I am confused. I am going to check the voltage next to see if its a low voltage problem. Any help would be greatly appreciated.
Thanks
John
Oh forgot to mention the clamp meter is reading just under 15amps with shower and fridge running.

 

[ProDave]

Voltage readings are the first ting needed.

 

[Andy™]

3kw shower... are you sure its not a hand wash?!

 

[SLIPSHOD & SLAPDASH]

What country is this ?

3kw shower... are you sure its not a hand wash?!

He could be a 'little person' 

 

[ProDave]

On a refurb recently, I removed a 5KW shower.  I thought that must be either cold, or a pathetic dribble.

Perhaps warmer places, who's cold incoming mains is a little more than 5 degrees C don't need so much heating for the shower?

 

[batty]

If they only give a 10 amp supply I would think its going to be a lack of adequate supply issue.

 

[SLIPSHOD & SLAPDASH]

I guess its Cypress  ;   they follow BS7671 & you pay for the supply available to you.  I have friends with apartments there who have a small supply to save money and turn the AC off to boil a kettle  or  using the washing machine etc.

Back to showers, i saw a 3kw one a couple of years ago. It did look like a hand wash, it was a cream metal canister about 100mm diameter in the 15mm feed to a fixed shower head. The landlord told me it had been there the 30 years    he had owned the place, was still working and no one had complained.

 

[Evans Electric]

I thought it was France TBH  .  And I'm thinking volt drop as I can't think of anything else.

 

[Marvo]

.......the fridge around 120watts max. 70 watts normal op.......

Are you sure the figures for the fridge consumption are correct? Domestic fridges are usually a bit more than that if it's a normal reciprocating/hermetic compressor. Maybe it's a very small one, 70watts normal operating power would make the compressor about 1/12th HP.

First thing to do is check the voltage at the fridge with the shower off then retest again with the shower running. 

 

[Constant Electrics]

Hi sorry but I just noticed that my post had been allowed. 

Cambodia is the country.

I checked the voltage it's 229 at the fridge (point). When the shower is running at 3 kw It drops  12 v  to 217 -  at 2 kw it drops 7 v This is from memory from a few days ago. Interestingly, the noise was less on the 2 kw setting and hardly noticeable on the 2 kw  than before Need to check at other times of the day I guess too..

They decided they needed a bigger fridge anyhow , so I will see what happens. I am still trying to track down a fridge protector with low and high voltage cut out . Not so easy to find at the moment. 

Yes the fridge is very small, like a hotel room fridge, slightly bigger. 

Would a loose neutral somewhere on the points circuit cause the prob? I am getting a slight (3v) reading on the points circuit neutral. I haven't had time to look at all the connections or unplug everything off the circuit, that's the next step.

I wouldn't have thought that the fridge would have any problems running at 217 v. (=/ - 6 per cent) 

I found out that the fridge had been in the rain last monsoon so although its working ok unless the shower is on, it maybe has issues itself. Any idea what that could be?

Yes, standard supply out here is only 10 amps! It has been upgraded to 20 at the house in question now. Of course you can get three phase, but no one wants to pay for it. It will take a few more years before the network is anywhere near western standard. 

Therefore: most showers out here are 2 - 4 kw! Lots of cheap hotels you see.

Thanks for your input

John

 

[SLIPSHOD & SLAPDASH]

What earthing arrangement do you use, could you check L to E when on load to compare with the N ?

 

[Constant Electrics]

Sorry , no earthing out here. I asked the customer if they required earthing but I think because everyone else hasn't got it she refused the extra expense.

What to do! 

 

[ProDave]

Measure the L-N voltage not at the point where the fridge plugs in, but as close to the incoming power feed as you can, i.e at the input to the main switch in your consumer unit.

If the voltage is still dropping there, then it's outside your control, i.e the network is not very robust.

If that remains relatively stable but the fridge is still dropping then you man have a poor connection in the house wiring somewhere.

I loop impedance test between incoming L and N would be interesting. I suspect it will be a very much higher reading that we are used to here in the UK

Perhaps if you are stuck with a poor supply, then you could just educate the occupants to turn the fridge off when using the shower, but don't forget to turn it back on again when finished.

 

[Marvo]

The voltage ranges you stated should be acceptable for the fridge although it might struggle to start if the start coincides with the shower being on and causes the voltage to drop to much less than 210v. 

 I am still trying to track down a fridge protector with low and high voltage cut out . Not so easy to find at the moment.

I wouldn't worry too much about supplementary over/under voltage protection for the fridge, if the compressor stalls due to low voltage or fails to start the thermal Klixon on the compressor itself should prevent damage.

 

[Constant Electrics]

Hi , I wish I had my Mega here. It would be good to use on this job, but fairly useless for circuits I haven't installed. Ever seen a consumer unit with only live wires?!! They joined all the neutrals (wired in red 6 mm singles for a 20 amp mains !) in the roof space. By joined I mean twisted, and if your lucky, taped. That was one snagging job I did, also they wired 2 live feeds to one master 2 pole  trip controlling lights /points in the kitchen. Anyone fancy opening an electrical college out here? ) 

I'll check the consumer unit incoming with the fridge running today and post the result.

Reading about Klixons, I'm guessing they are installed on all modern fridges, even cheap Chinese ones!?

looks like I will have to spend the time checking all the points to check the connections, there is no MK out here just very cheap Chinese outlets that cost .75 pence each! Anyone know where I can get reclaimed Crabtree/ Mk in smallish orders?

Once again, Thanks for your input, its much appreciated.

John

 

[Marvo]

Klixon is actually a tradename, thermal overload would have been a better term with hindsight. Anyway, usually the klixon is mounted on the compressor itself unless the fridge is running on one of the newfandangled isopropane gasses in which case if will be elsewhere. They generally look like this and as far as I know even the cheap Chinese compressors will have one;



If the compressor is a really small one then it may look like this;



Either way they have the same dual operation, they sense the actual temperature of the compressor dome and they detect the current to the compressor. If they trip they're auto-reset but they can take a while, sometimes as long as 20 mins for example depending on dome temperature.

.

 

[ProDave]

Sounds like classy wiring there. NOT

Do they use Screwits on their twisted connections?

Sounds like what we did about issue 1 or 2 of the wiring regs.

Talking of fridges, I have a freezer that acts very strange.  If you are near it when it starts, you hear a click. It hums for a minute. Another click and it's silent.  3 or 4 minutes later another click and it starts.

I have always believed the compressor is failing to start first try, the klixon trips, and on it's second try when it auto resets the compressor goes.

It's been like that from new, and is now 20 years old.  I tried to tell the shop it was faulty when still under guarantee, but met a brick wall because "it works"

I've been expecting it to fail, but it just goes on and on like that.

 

[Constant Electrics]

Hi, well I checked the voltage at the supply in, its reading is the same as on the points circuit when the fridge is on. So at least I don't need to spend all that time checking my connections.

Thanks for the low down and images Marvo, unfortunately I'm not authorized to view them , yet?

20 years is what I'd expect from a 90's build Dave. Funny how now that every things made in China it doesn't last that long. Been through 3 computers in the last 4 years!! Before that I only changed computer when it just got too slow. The customer is getting the new fridge tomorrow, Should be interesting. It must be the fridge I'm almost certain ) Lets see... 

John

 

[Marvo]

I also stay in a country where the national power supply is hanging by a ball-hair. Voltages here regularly drop to 190-195 during high load times but I've never heard of the symptoms you describe with your fridge. Usually if the voltage drops too low either the compressor just won't start or if it is running already it would stall. Either way the result would be the klixon tripping and the compressor power being disconnected.

........Talking of fridges, I have a freezer that acts very strange.  If you are near it when it starts, you hear a click. It hums for a minute. Another click and it's silent.  3 or 4 minutes later another click and it starts.

I have always believed the compressor is failing to start first try, the klixon trips, and on it's second try when it auto resets the compressor goes.

Sounds like the compressor s failing to start first time as you say. Often caused by the 'off' time being to short and not allowing the refrigeration system to equalise, domestic compressors especially are poor at starting under any kind of load ie whilst there's a pressure difference across them. The constant cycling on the klixon will probably eventually take it's toll on the klixon itself..
Glass door display fridges are especially prone to this because the heat loss through the glass is higher therefore the internal temperature rises quicker therefore the compressor restarts sooner. Gaps in the door seals can cause similar problems with domestic fridges, also if they're set too low the higher temperature gradient across the insulation causes higher heat loss and quicker internal temperature swings. The differential on the t/stat might be a bit short or something like the internal light staying on with the door closed could also cause it.

 

[Constant Electrics]

Well, the drama continues... They bought a new LG waited 24hrs then plugged it in. They noticed it was getting so hot on the transom between the freezer and fridge they unplugged it. I was there when they did this and it was, I think, too hot. Couldn't keep my fingers on it for long.

I guessed it is a faulty fan. They are supposed to take it back today. Oh, by the way it runs fairly silent as it should.

No screwits out here, wouldn't be so bad if there were.I quite like them as you get a good connection. Haven't seen them for a few years now.

More later..