# Amps and volts to watts: conversion

Another matter to consider:
For a long time, also, I have had a power strip in my room, with a nice thick cord, plugged into a wall outlet (3-hole) near my night stand. Plugged into it are a small digital alarm clock, a 40 - watt reading lamp, a power cord for my hospital-type bed, and a radiator-shaped heater (oil-filled) which uses 1875 watts. I NEVER leave the heater running unattended, never have it running when I am in bed, and never operate the bed controls with the heater on. I have never had any problems with the heater. For quite a few years now.

Do you have 20 amp circuits? 1875 watts is more than you should be able to draw from a standard 15-amp receptacle.

I don’t know the amperage; the mobile home, a double-wide, was built in 1961.

A 20 amp outlet has a T shaped slot on one side, as opposed to a 15 amp outlet which has straight slots on both sides.

See here:

Bottom line:

1. If your heater dissipates 1875 watts then the current is 15.6 A.

2. According to the NEC, “The rating of any one cord-and-plug-connected utilization equipment not fastened in place shall not exceed 80 percent of the branch-circuit ampere rating.”

3. Is the branch circuit rated for 15 A (14 AWG wire in the walls) or 20 A (12 AWG wire in the walls and 20 A circuit breaker)? If it’s a 15 A circuit, then you’re not allowed to plug a device into a receptacle that draws more than 12 A (> 1440 W), which means you should not plug this heater into any receptacle on this circuit. If it’s a 20 A circuit, then you’re not allowed to plug a device into a receptacle that draws more than 16 A (> 1920 W), which means you can plug this heater into any receptacle on this circuit.

4. Never plug a “high current” device into a power strip, regardless of anything else. Your heater is a high current device.

5. If you need to use an extension cord with your heater, make sure it uses 12 AWG wire. Something like this.

Hmmmmm…I’ve never seen anything like that in a mobile home, especially as old as ours. Our outlets’ holes have straight sides, even the outlets with 3 holes.

is this 1965 or something?

As I noted upthread, our mobile home was built in 1961.

Last night I switched the heater on, as I had been doing every night for the last few months. It still had its power cord plugged into a power strip; the strip’s capacity I calculated at 1800 watts (only this morning!) and the heater–which I did not have running at full capacity–uses as much as 1875 watts. The only other thing using the same power strip was a small electric clock.
When I when to switch the heater off I noticed that the buttons were dark, which usually means the unit is off. I thought that was strange. Then I went to switch the light on my night stand on; it wouldn’t light! I thought the bulb was burned out. It wasn’t.
To make a long story short: The heater’s current, after all these months, had blown the power strip (the clock was not running, either); the red button on the strip was frozen. I figured it had been blown, and removed it. It’s shot. The clock, lamp, and heater are intact. I have also found that the heater cord will reach directly to the wall outlet.

how did you calculate the power strip’s capacity?

From the voltage and amperage information embossed on the bottom.

Your power strip gave out before your house caught fire … lucky I’d say. The portable electric heater I use has different power settings and I never use anything above 500W, not in this old mobile home. The two main heaters are hard wired with 10 gauge romex that I installed about 15 years ago.

I’d advise hiring an electrician to look things over, maybe pull some new wire … and make sure your smoke alarms are working.

A lot of good discussion so far.

One thing missing in this discussion is the in-rush current. The posted amperage or the wattage of the heater is for the steady operation - that is when the element is hot. Depending on the material of the heating element and the quality control of the manufacturer, the current draw (and the power draw) when it is turned on can be significantly high.

This is also the case for incandescent lamps. While the incandescent lamp took a fraction of a second to get to the operating temperature, the heater takes several seconds: thereby causing the electrical wires to heat up significantly.

I wouldn’t give that any weight. you’d have to bust it open and look at how it’s wired internally to determine what current level is safe. I’ve seen some cheap-ass ones which had like 18 gauge wire inside. Some of them might have stamped brass/copper “bus bars” between the individual sockets, but you’d have to measure the thickness and width to determine the equivalent wire gauge.

If a power strip is rated at 15A, and UL listed, I’d have no problems with plugging in a 12A heater. Are you saying UL listing is just a scam to generate money? Say it ain’t so!

I’ll do nothing of the kind. I check these things out in the store. If I tried “busting open” a power strip in a store I’d wind up in jail, or sued, or both. I have no electrical expertise–in fact, the only real knowledge of electrical things I have is what I gleaned on this message board. So maybe you had better choose your words more carefully.

I have a power strip rated for 15 A. I took it apart. As you can see, the hot contacts for the six receptacles are tied together using a stamped, elongated metal strip. There’s an identically-looking strip used for the neutral contacts. Each strip contains spring tabs for making electrical connections to the prongs of each plug. It looks like the spring tabs are made using a punch and die.

I don’t know what the strips are made of. They look like they’re brass, though I’m not sure if they’re solid brass or if they’re solid copper with some kind of plating (brass or nickel plating?).

There is a UL sticker on the enclosure. I assume this means it complies with UL 1363, which also means each of the six receptacles must meet UL 498 requirements. According to UL 1363, if a 15 A load is plugged into one of the six receptacles, the temperature rise of the electrical contacts should not exceed 30 °C above ambient.

So yea, my power strip should be O.K. when the load current is 15 A. But something still bothers me about it. I have heard quite a few stories (albeit anecdotal) about power strips melting or catching fire. Regular 120 V / 15 A wall receptacles (NEMA 5-15R / UL 498) do not seem to have this reputation.

On the basis of Crafter Man’s statement I am confident that the information I have about the power strip and its capacity is adequate and obviates the need to disassemble it.

You are displaying remarkable common sense, lacking in many who are destined to become, or already are, of the insidious engineering persuasion.

Funny. Reading Crafter Man’s post makes me want to take a power strip apart. Maybe see if I can improve it.

Insidious. A good description. Curiosity is so inviting…

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