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My home has a strict limit of 45 Amps, for what I can use. I assume this means I cannot draw more than 45A at any point in time, otherwise the fusebox will jump?

I know I am close to this limit, because when I was at a lower Amps rating, I had to ask my electricity provider to increase it. 45 Amps is the maximum I can have with my current installation.

I need to install an electrical water heater (to replace a gas one). Before I do so, I want to make sure I understand how many amps it will draw. It says "power 2000W". Given that my country has 230V, does it mean that it will use 8.7 A (2000 / 230) ?

That's what would make sense to me, but I am getting quite confused after searches on the internet that say the power indicated on an appliance does not necessarily translate into power drawn from my electrical circuit. If someone can explain why that is, that'd be fantastic.

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  • I believe that the "power indicated does not equal power drawn" references the fact that the name plate shows the maximum power the appliance will draw, and is not a guaranteed, constant load. When your water heater is running, it will probably draw the max power all the time. However, if you're using a mixer, it will draw a high current as the motor starts, but the draw will drop once it's running - especially if it's not set on max power. When provisioning, you have to account for the max usage, though. Wait for the electricians to give you a 100% confirmed answer, though.
    – FreeMan
    Jan 14, 2021 at 11:56
  • Ok, thank you, that's useful.
    – DevShark
    Jan 14, 2021 at 11:57

2 Answers 2

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You need to read the nameplates on your appliances. They will state either

  • Amps (preferably), which you can use directly
  • VA (hopefully) which you can divide by 230 to get amps. Or
  • Watts, which if it is a resistance heater you can divide by 230 to get amps, but if it's any sort of electronics or motor driven load, all bets are off.

The difference is, AC power is a sinewave. Heater loads use the entire sinewave very consistently, so it's easy to get amps from watts. However, motors and electronics draw power unevenly: we must size supply equipment for amps, not watts. VA is "the watts you must size for".

But at the risk of stating the obvious, you only need to think about appliances that are running at the same time. If you don't run your air conditioner and your heater at the same time, you don't need to figure for both of them.

Keep in mind 2000W is a very small water heater. If it is an "on demand" unit, expect no more than 1.5 litres per minute of usable hot water, so you won't be taking a shower with that. If it is a "tanked" unit, except a long recovery time along similar lines.

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  • Thanks for that. "if it's any sort of electronics or motor driven load, all bets are off" -> can the actual power used be higher? Or is it always lower than the displayed value?
    – DevShark
    Jan 15, 2021 at 0:32
  • Yes, watts is always <= VA. An illustrative example of VA is a 60 watt incandescent bulb in series with a diode. It lights during the positive half of the AC cycle and does not light during the negative half. It draws 100% of the current, 50% of the time. Watts 30 VA 60. Jan 15, 2021 at 1:02
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Yes, the amperage draw for your 2000 watt water heater will be about 8.7 amps. To calculate the amperage of any heating element divide the watts by the voltage. If the amperage draw is too high for your application, you could exchange the heating element with a lower wattage element. Hope this helps.

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