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So we've been renovating (virtually new everything) a 1930s semi that hasn't been modernised since it was built and hadnt been lived in since the 70s. Naturally a full rewire was high on the agenda which is 90% complete now, but my suspicion began when the 3000W fan heater I bought seemed not to be chucking out much heat. At first I thought nothing of it putting it down to a poor quality appliance. But when a new kettle I tried took around 7minutes to boil, I started pondering if there was a fault somewhere causing a limit to max power these appliances were generating/drawing. I had the plugs tested and they are producing 230v but before researching ohms law, I suspected a resistance issue. To double check, I took the heater home and plugged it in and hey presto, belting hot heat. I am awaiting an updated fuse board from Northern Power, which I'm sure will fix the issue but, I wanted to rule out any problem with my installation before I sign off with the sparky ideally.

The only other info I have is the original power was a shared supply to ours and next door and I wondered if some sort of phase drop was present grid side of our board. Is my next logical step testing resistance between board and consumer unit? Can you do that with a normal multimeter? My electrician who looks to have done a fantastic installation seems to be brushing it off like there's no problem but the house will be electrically heated and rented out so I can't have 2k worth of underperforming rads getting overworked.

All ideas, practical and theoretical appreciated. Sorry for essay.

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    \$\begingroup\$ Buy yourself a cheapy plug in energy monitor. It will tell you volts, amps and Watts at the outlet. No need to fiddle with dangerous electricity and you get hard numbers. You can try it with a load, without a load or any outlet. \$\endgroup\$
    – Kartman
    Commented Mar 8, 2021 at 1:19
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    \$\begingroup\$ One -- you'll get better answers on the DIY stackexchange; we're a bunch of engineers that know theory, and may or may not know practical applications. There's Real Live Electricians that hang out on the DIY stackexchange. Two -- @Kartman, that sounds like an answer to me, however short. Feel free to make it one. If you do the test with load, and you see a significant drop from 230V with a load, then that's good evidence that there's a real problem. I wouldn't let the electrician rest until it was either fixed, or proven to be present at fuse panel (and thus the power company's problem). \$\endgroup\$
    – TimWescott
    Commented Mar 8, 2021 at 1:27
  • \$\begingroup\$ Hmm you haven't mentioned wire guage. What guage wire was used for how many amp circuits? Are there any particularly long runs in the house? Has the electrical inspector already been and gone? Do all plugs perform the same with the same load? 3kW is more than 80% load for a 15 amp 230V circuit. Are you using a 20A circuit or a 100% rated breaker? \$\endgroup\$
    – K H
    Commented Mar 8, 2021 at 2:32
  • \$\begingroup\$ Something else too look out for: in the 1930s, to save money, houses sometimes shared common neutrals on different phases so that the return current would be lower than the incoming current (so they could use fewer wires when wiring the house). That's fine, and even up to modern electrical code. The problem happens when homeowners don't know that and move circuits between phases. That could result in over voltage on some circuits or tripping fuses, or overloading neutrals. You might need a real electrician (not us electrical engineers) to help with that though! \$\endgroup\$
    – KD9PDP
    Commented Mar 8, 2021 at 4:59

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mains monitor

Get yourself something like this. It should tell you Volts, Amps, Watts etc. the picture is only to describe the type of widget I’m referring to, not a specific product recommendation.

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  • \$\begingroup\$ Pictures still need to be sourced, though. \$\endgroup\$
    – Hearth
    Commented Mar 8, 2021 at 4:40
  • \$\begingroup\$ Thanks for all replies. All noted and will be put to the electrician whos coming over with testing gear today. Especially the point about the shared neutrals, I feel this is pertinent to my situation. No long runs its just a 3 bed semi and with about 5 different ring mains (think that's what they're called). I will plug it into the heating circuit that will go live today to further eminate an ampage issue. Will report back for those curious. \$\endgroup\$
    – StvC
    Commented Mar 8, 2021 at 8:44

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