Electrical Anomally. Mains Power.

[Formaleins]

I posted not long back about replacing cables from the meter to my house after some storm damage. At the moment the main cable (25mm SQ) that we are using was snapped like a carrot in two places (It is Aluminium), some guys repaired it and it is joined by twisting tightly together using a couple of pieces of additional cable - same gauge. Haven't got around to repairing completely as I am still fixing the roof damage.

 

Ever since the cable was broken then repaired I am seeing some weird behaviour on my 8KW water heater. Normally (before damage) the heater when it was set to 5KW would heat the water pretty hot within about 2 minutes of firing up, now it is taking over 5 minutes to even get anywhere near the original temperatures.

 

The water temperature entering the heater has not changed. I have checked the voltage and voltage drop of the main cable when it enters the consumer unit with the shower on and off and there is virtually no difference from before, generally drops from about 227V to around 211 volts at 8KW. This has always been the case. (in fact it used to be a LOT worse!)

 

Any idea what could have changed? Is it possible that there maybe individual strands within the cable that may have broke due to the stress when the cable was snapped? (It snapped it clean into 3 lengths) Could some of these conductors be broken but still covered by the insulation? - Would that even give me this effect, I assumed that if there was a decrease in the power the cable could handle that there would also be a comparable voltage drop that I would have measured.

 

Any ideas?

 

Cheers.

[Crossy]

The supply isn't collapsing so you have a reasonable connection to the outside world.

 

Can you check the current being drawn by the heater? (is it actually drawing the rated power)

 

It's possible that the storm damaged the heater controls / element.

 

Do you have a second water heater you can use as a load?

 

[Formaleins]

3 hours ago, Crossy said:

The supply isn't collapsing so you have a reasonable connection to the outside world.

 

Can you check the current being drawn by the heater? (is it actually drawing the rated power)

 

It's possible that the storm damaged the heater controls / element.

 

Do you have a second water heater you can use as a load?

 

Cheers Crossy, the heater seems fine, I have another 4.5KW shower heater on a separate circuit and it is doing the exact same thing, taking ages to get warm but once up to temperature it is fine as well. Unfortunately got nothing heavy enough any more to test the current, my old Fluke bails at 20A for a short test.

Edited May 14, 2019 by Formaleins

[Crossy]

Hmmm. Can you check the voltage at the heater in operating and non-operating conditions?

 

Evidently the power is getting lost somewhere, or you have become more fussy of water temperature.

 

[Formaleins]

1 hour ago, Crossy said:

Hmmm. Can you check the voltage at the heater in operating and non-operating conditions?

 

Evidently the power is getting lost somewhere, or you have become more fussy of water temperature.

 

OK, done that - 227 heater off, 209 @ 8KW and 216 @ (I think) 6KW

[Crossy]

2 minutes ago, Formaleins said:

OK, done that - 227 heater off, 209 @ 8KW and 216 @ (I think) 6KW

 

Nowt wrong with those readings.

 

So, either the heater is not developing its full output (fried electronics or an element). Or something else has changed (inlet water temperature maybe).

 

With no means of measuring current or power I think we could be stuck, does your meter do AC amps (many cheap ones don't)?

 

It's odd that two heaters are exhibiting the same symptoms if it's a heater fault.

[Formaleins]

55 minutes ago, Crossy said:

 

Nowt wrong with those readings.

 

So, either the heater is not developing its full output (fried electronics or an element). Or something else has changed (inlet water temperature maybe).

 

With no means of measuring current or power I think we could be stuck, does your meter do AC amps (many cheap ones don't)?

 

It's odd that two heaters are exhibiting the same symptoms if it's a heater fault.

Yes, the Fluke 87 III will measure AC Amps. but normally 10A and 20A for a few seconds before it needs a new expensive fuse!

[Crossy]

49 minutes ago, Formaleins said:

Yes, the Fluke 87 III will measure AC Amps. but normally 10A and 20A for a few seconds before it needs a new expensive fuse!

 

Time to go shopping for a cheap clamp-on meter methinks. Always a handy thing to have, save the Fluke for those important jobs ????

 

[Fruit Trader]

With no other appliances adding load, you should provide the voltage drop value at the point where heater is turned on and five minutes later at the point where it starts to produce satisfactory temperature.

 

This will show if the heater is making any power adjustments during or towards the end of warm up period. If it is not then the sudden rise in outlet temperature must be down to a change in inlet temperature or flow.

[bankruatsteve]

Is your water flow same as before?  Maybe try backing off on the flow until hot. Also, is there a chance your heaters have "calcified"?  Not sure what that would do to the element.  Just throwing stuff out there.

[Formaleins]

15 hours ago, bankruatsteve said:

Is your water flow same as before?  Maybe try backing off on the flow until hot. Also, is there a chance your heaters have "calcified"?  Not sure what that would do to the element.  Just throwing stuff out there.

Thanks guys! apologies for the late reply but we lost the internet yesterday.

 

The waterflow is pretty much the same as before, it varies a small amount but nothing that significant as we use two storage tanks which then go to our pump.

16 hours ago, Fruit Trader said:

With no other appliances adding load, you should provide the voltage drop value at the point where heater is turned on and five minutes later at the point where it starts to produce satisfactory temperature.

 

This will show if the heater is making any power adjustments during or towards the end of warm up period. If it is not then the sudden rise in outlet temperature must be down to a change in inlet temperature or flow.

Thanks, excellent idea - I tried it and there is no change in voltage drop at all between power on and when temperature rises. Maybe I am just going mad?

[Crossy]

2 minutes ago, Formaleins said:

Maybe I am just going mad?

 

You said it