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ge_meterPhoto by neil lall

I will try to keep this simple and non-technical.

Electric power delivered over lines by Domlec (the Dominica Electricity Company) is the same as used in the UK: 230Vac*, 50Hz, single-phase.

Vac means volts, alternating current. UK voltage can be anything between 220Vac and 240Vac, I will use the nominal value of 230Vac. Similarly, US voltage can be between 110Vac and 120Vac, and I’ll use the value of 115Vac in this article.

This is different from US electrical grid power in all three respects:

  • The US voltage is only half as much: 115Vac*. This is very important.
  • The UK frequency of the alternating current is 50 Hz (Hz = cycles per second) and the US used 60Hz power. This is usually not very important.
  • The UK hookup is single-phase. It uses only three wires; live, neutral, and earth (a/k/a ground). The US hookup uses four wires; 2 live phase wires, neutral (a/k/a common) and ground. This is very important.
  • The neutral and common are not connected together in at the circuit breaker box in UK hookups; the earth wire is separate all the way to a ground rod. In the US hookup, common and ground are connected at the breaker box. This is only important to know if you’re wiring you own house.

You generally can’t use any US 220V appliance on UK voltage because in the US the 220V is derived by bridging the two 110V phases (which run 180° out of phase with one another), but the common wire is also brought in through the plug, meaning that the appliance maker may internally (you generally have no way of knowing unless you can obtain, and read, the electrical schematic drawings) tap 110V between one phase and common. They do that with 220V clothes dryers – only the heater is 220V, the motor & control circuits are 110V; if you connected a US 220V dryer to a UK 220V outlet, its motor and control circuits would immediately burn out, possibly with sparks and flames.

You can use a transformer to step UK voltage down to US voltage. There are two things you must know:

(1).You must know the wattage that you wish to take from the transformer (that is very important), and (2).You must remember that the transformer does not change frequency, so the output will be 115Vac 50Hz (not 60Hz, but it’s seldom important).

Fortunately, wattages are usually written on appliances (and light bulbs). If not, wattage is very easily to calculate: Look at the appliance label. If it does not give the wattage directly, it will give the current (Amps, or Amperes, or Amperage) used. Wattage is simply volts (used by the appliance) times amps (used by the appliance). For example a US 120V 15 amp power saw uses 120V times 15 Amps = 1800 Watts.

The transformer therefore must have 1800W or greater output. If you try to draw more power from a transformer than its rating, it will burn out. Also fortunately, Wattages simply add. That is, a 2000W transformer can support any number of units on its output as long as the sum of their Wattages is 2000 or less.

Frequency only matters when the device has AC motors, which rotate synchronously according to the frequency. Most DVD players, etc have internal power supplies that convert the input AC power to direct current (DC) and use DC motors. So’ they’ll work through a transformer. But 50Hz is 5/6 of 60Hz; an clock will run slowly and a 3600 RPM saw will run at 3000 RPM (usually good enough).

To keep things simple for my wife, I do the following, which I suggest you do too:

  • Label the wattage of each appliance. I use masking or adhesive tape and a marker
  • .

  • If the appliance is 220Vac only, attach a UK-style plug to it. (More about how to do that later.)
  • If the appliance is automatic (self-detecting) 110/220Vac leave the US plug on it and write “dual” on the tape.
  • If the appliance can operate at either 110Vac or 220Vac but must be manually switched to the proper operating voltage, write “switched” on the label & make certain the user knows which voltage to plug it into. I suggest not changing the plug unless the appliance is not one that gets moved about.
  • Screw-in bulbs have the same size bases in the US and UK (and the rest of the world); convert all lamps to have UK-style plugs and use only 220Vac bulbs; which can be incandescent, energy-saving compact florescent, or (if you can get them) super energy efficient light-emitting diodes (LEDs).

A transformer is a converter: it changes one voltage to another. You can also purchase adapters. An adapter does not change any voltage; it simply changes the mechanical configuration of an outlet so that it can accept a differently-shaped plug. You would plug a dual (or switchable) voltage appliance with a US plug into a Dominican UK outlet by using an adapter. You can buy adapters in many stores in Dominica.

I suggested putting a UK-style plug on 220Vac (or dual & switchable, but not normally moved) appliances. Sometimes you’ll buy a 220Vac appliance made for a 220Vac-using country other than the UK, and it will have a non-UK-style plug. Here is how you do that. You can buy plugs in many stores in Dominica.

  • Cut the original plug off.
  • Strip the wire ends.
  • The UK and the rest of the world (except the US/Canada) use the following color code:
  • The live wire is brown. (In the US it’s usually black; if both phases are used, one live will be black and the other red.)
  • Neutral (common) is blue. (In the US, it’s white.)
  • Earth (ground) is green or yellow & green. (in the US it’s green.)

The UK-style plugs are labeled L/N/E at each terminal. Also, the L (live) terminal is normally fused in the plug.

When you change a lamp plug, use a continuity tester or ohmmeter to ensure that the L wire is connected to the internal “button” connection inside the screw-base and the N wire is connected to the outside of the base. If the lamp has a 2-prong polarized plug, the wide prong is the neutral/common.

Power here tends to be unreliable. We have a small 120Vac generator. We use it to prevent loss of the contents of our refrigerator/freezer. But that appliance is a 220Vac one. However, any transformer can work in either direction: If it is a 2 to one transformer it can step 220Vac down to 110Vac or step 110Vac up to 220Vac. You simply must know how to make the transformer connections. And you must know the wattage output of your generator. (A transformer’s wattage is the same whether stepping up or down.) And you must know that the appliance doesn’t have a long “surge” wattage – all motor appliances have surge; you can usually find it in the label or on-line spec’s, and that the appliance can tolerate 60Hz power.

Finally, I suggest you obtain a UK-style surge protector to wire in at your circuit breaker box and use additional plug-in surge protectors on critical appliances. (Before we did the latter a surge on Domlec power blew the electronic control circuit board in our refrigerator. It took 15 days – and cost Domlec EC$1049 – repair.

We had to use a friend’s freezer and move a small refrigerator upstairs meanwhile.) When power goes out if possible unplug always-on items like your refrigerator and plug then back in after power returns. And, a transformer provides some additional surge protection to those 110Vac units. But a transformer can’t be 100% efficient and wastes some power. That’s especially true here because most transformers are tuned for 60Hz and the 50Hz current here makes them less efficient. Domlec says that a 2000W transformer wastes EC$100 of power per month; but that’s nonsense: We have an always-on 5000W transformer for the upstairs of our villa and our total electric bill has never been over EC$100. Still, we turn off the 1500W transformer in our downstairs laundry room (or with my generator when needed) when we’re not using the washing machine.

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