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Question

Is there a maximum limit to mains frequency range that appliances will accept (e.g. if they conform to UK or EU standards?)

e.g. The Dynamic Demand web site indicates that there is a legal limit of about 49.5 Hz to 50.75 Hz (lines on the meter).

Why?

I'm configuring an Amber Switch (CAS-I-B) to turn on/off a hot water if the mains frequency is increased/decreased respectively, which in turn is performed by the inverter if the batteries are fully charged.

Note: the inverter is powered by a DC solar/battery system (no grid tie).

I'd like to increase the frequency to 53.5 Hz or even higher, but before doing that, wanted to know what the official limits are. Obviously individual appliances may be higher, as they could be manufactured to operate in countries with lower quality power. What kind of appliances should look out for in particular that are likely to be a constraint?

My guess is that AC motors are the most likely culprit as the higher frequency may make them run faster, so around the house that would be water pumps, refigerators and plug-in vacuum cleaners.

What is the most likely 'damage to equipment' one would see with wildly varying mains frequencies?

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    \$\begingroup\$ Higher frequencies are not a problem electrically, it's lower frequencies that are. Because they require bigger transformers/iron parts of AC motors. The higher frequency will affect your water pumps and your fridge because they have AC motors but it's unlikely to matter mechanically within a +10% margin. Your vacuum cleaner has a DC motor so it doesn't affect it at all. \$\endgroup\$
    – Janka
    Commented May 26, 2017 at 22:15
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    \$\begingroup\$ Since many countries use 60 Hz, check the label of the item you are concerned about. It may be 50-60 Hz. \$\endgroup\$
    – Brian Carlton
    Commented May 26, 2017 at 23:24
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    \$\begingroup\$ The legal limit is 50.00Hz \$\pm\$1% [save in abnormal or exceptional circumstances]. nationalgrid \$\endgroup\$
    – StainlessSteelRat
    Commented May 27, 2017 at 1:01
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    \$\begingroup\$ In the old days, at least in the US, the long term average frequency of the grid was extremely accurate. If it ran a little fast, the operators would keep track and slow it down a bit to make up for it, so that the number of cycles per day was very accurate. One reason they did this is that a lot of clocks used to effectively use the grid 60 Hz as their frequency reference. I don't know if this is much of an issue nowadays. Not sure that many clocks use the grid for a frequency reference. \$\endgroup\$
    – user57037
    Commented May 27, 2017 at 7:04
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    \$\begingroup\$ First of all you should think how you're going to wire your inverter to your existing mains wiring. Will you disconnect the utility network (hint - you should!) and if so can you get a signal from it. When the utility power is down you (or some automated switch) should break the circuit and then fire up the inverter. Getting a signal from this automated switch you can pass it to the switch that turns off your water heater. Otherwise you will try (of course without much success) to power up your neighbours with your inverter. \$\endgroup\$
    – Todor Simeonov
    Commented May 27, 2017 at 10:41

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Amber Switches are not needed to protect the loads but are exclusively designed for "islander" renewable low power generators with no energy storage.

The spec here is load regulated generator frequency which lowers in RPM or Hz under high loads and rises above norm, with low loads.

If you are not the owner of the grid and live in the U.k. where the freq. tolerance is adequate, there is no purpose to be served here.

Unless you are participating in "load shedding" for reduced rates, there is no need to do this.

The Amber Switch has a hysteresis of 0.25 Hz which can be set to a very limited range value for 50 or 60Hz

Therefore your requirement is unnecessary.

Keep in mind heavy motor loads are 5 to 8x rated full power when switched ON unless custom low surge designed. This is far greater than a 5% frequency change that occurs very slowly or even a 1~2 swing as noted in the UK. Here in Toronto, we can sync our OCXO's to the grid.(lol)

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  • \$\begingroup\$ I have edited my question to emphasise that, I'm off grid, and am using the 'Independent' rather than 'Load Shedding' model. The switch goes on/off sooner if the frequency difference is higher. Currently it set to 51.75Hz, so it goes off very quickly when the frequency drops down to 50.00 Hz, but at 52.00 Hz, takes longer to come on again, by which time the solar charger has gone past its float voltage, throttling back production for the rest of the day... \$\endgroup\$
    – xirt
    Commented May 27, 2017 at 14:46

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