Electricians - OK to Use Stranded on 220 / 60 single Phase?

I am again replacing a pool pump (don’t ask).

The motor is uprated at 1.5 HP, pulling 10 amps.

The custom is to use solid core wire - which, I found out cannot be bent while connected without breaking the flimsy plastic terminal board.

Hence the idea of switching to stranded.

I know about the differences in cooling characteristics between AC and DC (AC’s on/off pulses serve to cool the wire - DC is always hot - this is why your house uses solid (cheaper) and your car uses stranded (greater surface area for cooling)).

Is there something about heavy motors which require solid, or are the installers just being cheap?

The distance from the switch to the motor is approx. 6’.

First of all, the idea that there is some difference in “cooling” between AC and DC is wrong. It’s the average current that’s important - a wire is going to get just as hot carrying 10A of AC as it is with DC. Solid wire is used because it is cheaper and smaller than stranded for a given AWG. There’s no reaon that I can think of not to use stranded wire in this case.

Another option to consider might be terminal lugs at the end of your wires. Then you could use either solid or stranded conductors.

stranded can be bent easier and is useful for that purpose. form the wire to lay the way you want before attaching.

Same gauge, same capacity for power conductors. Use whichever you like.

You should be able to pigtail a short piece of stranded to the solid wire, which I assume the solid wire is already bought and already run. Perhaps a 6-8 in piece of stranded connecting to the circuit board then wire nutted to the solid.

Also I think cars use stranded because of vibration and flexing that is experienced in wires in cars. The engine moves quite a bit on it’s motor mounts and wires and tubing need to be able to flex - stranded works better for that.

But car cables have terminal lugs at the ends, as t-bonham mentioned.

The main problem with stranded wires is that, inevitably, when you tighten the terminal some strands will get cut, effectively reducing the cable’s gauge.

Another problem is that stranded cables are much more prone to corrosion. A solid core wire might corrode a little at the surface but otherwise it will be fine.

When we measure (eg. with a clamp meter) 10A of AC current, this is actually the peak current. For most of the AC cycle the actual current is goign to be a value smaller than 10A (the peak value).

So yes, 10A of AC is not equivallent to 10A of DC. When measuring heating effects we use the RMS value. 10A of AC is actually equivalent to 10/sqrt(2) = 7.07A DC

The thing to watch is some terminals aren’t rated for stranded wire.

This is incorrect.
All normal AC current meters are calibrated to read RMS current, witch is exactly equal to the heating capacity of the same value of DC current. In other words, 10A AC RMS will have the same average current as 10A DC, although the peak value of the AC current will be 14.14A, and the minimum value of the AC current will be zero.

Your typical AC meter reads rms values, not peak. I’ve only seen peak values on fairly fancy (and expensive) meters and even those did rms by default.

The wire needs to be rated for the rms current (or the DC current) but the insulation has to be rated for the peak voltage. The typical wire you buy at home depot and the like will be designed for AC use and will have an adequate insulation rating.

As for the OP, using stranded wire is fine. I’d be tempted to put a terminal lug on it, as was already mentioned.

AC actually has a slightly higher heating effect than DC if you consider the average current (not RMS, average), since for AC, RMS is 0.707 of the peak and average is 0.636 of the peak; thus, 10 A RMS is only 9 A average (RMS is used because that gives the equivalent power; 10 A RMS at 120 volts RMS is 1.2 kW, same as 10 A average at 120 volts DC). This is irrelevant though since RMS is almost always used for AC.

Also, as previously mentioned, stranded wire can cause some problems depending on the connection; for example, if you try to connect it to a screw terminal (as on receptacles), the wire will spread out and not make a good connection, and you’ll have loose strands coming out, unless you connected a terminal lug to it.

The average voltage (and current) for a sinusoidal signal is zero.

That depends on how you define “average”, since as my link shows, you can calculate an “average” voltage for a sine wave, although it obviously isn’t an “average” as taken in the usual sense; the only way to actually measure it would be to use a bridge rectifier and measure the output voltage (adding 1 volt or so for diode drop) with a DC meter.

Ignorance fought then. But those clamp meters still show peak value for voltage, don’t they?

This is not correct.

The wire that is used in your house, particularly the 10 , 12, and 14 AWG “Romex” stuff, is solid because solid works better than stranded when tightening the wire under a screw head. It is also cheaper to manufacture than stranded wire.

For the most part, stranded wire is used when you need the wire to be flexible. One good example is jumper cables. Could you imagine what they would be like if the wires were constructed of solid copper? As for vehicles, stranded wire is used for the following reasons:

  1. A vehicle’s wiring system contains dozens of electrical connectors to facilitate convenient replacement of computers, motors, sensors, lights, solenoids, etc. Solid wire and connectors don’t mix. Plugging/unplugging the connector puts a lot of bending torque on the wire, which will quickly cause a fatigue failure (i.e. a break) in a solid wire.

  2. Wire in a vehicle is subjected to lots of vibration. Stranded wire can easily absorb these stresses.

  3. Routing the wiring harness in a vehicle would be a pain in the ass if all the wires were solid.

Nearly all meters designed to be used with residential AC read in RMS.
The only folks interested in peak readings are engineers, and even they can get the peak reading from the RMS by multiplying by 1.414. Things are different for non-sinusoidal waveforms, but they are not generally encountered by electricians.

When they talk about “average,” they’re talking about the average value for a sine wave that is full-wave rectified. It’s not important for most applications. When talking about average power, the key parameters are RMS voltage and RMS current. Other things are also important, like phase angle, but that only muddies the issue.

Well, now that we’re talking about it… :wink:

Cheap meters measure “RMS voltage” and “RMS current” by measuring the peak value and dividing by sqrt(2). This works O.K. if it is a sine wave. Does not work when it is not a sine wave. It is usually not an issue when you’re using the meter for measuring 120 VAC in your home, since the voltage maintains a pretty a good sine wave shape regardless of what’s going on. But it can become problematic when you’re using the meter to measure RMS current, since the current waveform can look pretty wacky.

For this reason, more expensive meters measure true RMS voltage and true RMS current. They do it by sampling the waveform.