Starting current exceeding 16A

[alphacat]

Hey guys.

I wanted to ask an additional question about starting current exceeding 16Arms.

The wires of most wall outlets are designed to conduct max. 16Arms.
Its even written on the outlet itself - " 16A ".

Doesnt a starting current above 16Arms damage the wires/outlet?

Or the fact that it only lasts a few seconds makes it not to damage the wires/outlet?
(I'm not sure if a few seconds are considered a long time or not).

Thank you.

 

[smanches]

It's all about how much heat it's going to generate in the wires. They have rated it at 16A @ because that creates a certain amount of rise in temperature. You can push more through them, but the temp is going to go higher. I'm sure you could find a calculator online that would allow you to calculate the temp rise in the wire for the surge you're looking at. The length of the wire run also affects it, as that's going to increase resistance. I'm not sure at what length they rate wire amperage. It's always bugged me.

 

[Sceadwian]

The length of the wire run does no affect the maximum current that can be carried, it does however cause a voltage drop which needs to be calculated, if the run is too long the voltage under full load will drop, this can be very bad for electric motors if the voltage drop is too much. There are calculators out there that allow you to figurethe voltage drop at a rated current over a given size of wire.

smanches to think of the reason why the wire length doesn't effect the current they figure the thickness of wire for the wire based on power dissipation over a small length of wire. If that power dissipation is too high the wire will melt, if it's in the right range it'll just heat slightly, how long the wire doesn't matter, though the increased overall power dissipation will cause the voltage to drop. The amperage ratings for housing wiring are based on standard home construction methods to keep heating in the walls from getting too high.

Higher pulse currents will not harm an outlet or the wiring as long as they are short, however they may trip the breaker, the higher over 100% of a breakers rated current you go the faster it will trip so it depends on what your starting current actually is. Since this is a starting current issue I'm assuming the load is a motor? You have to keep in mind what might happen if the motor is stalled with a locked rotor, basically the starting current would be stuck on. If your buildings electrical system is designed properly it should do nothing more than trip the breaker, but do not allow this to occur.

 

[alphacat]

Thanks guys.
I'm not to design by myself an housing wiring, but rather want to understand how the existing housing wiring handles high starting current above 16A.

The amperage ratings for housing wiring are based on standard home construction methods to keep heating in the walls from getting too high.

So if an wall outlet is 16Arms rated, it could still handle a starting current of say 22A?
(Yes, i'm talking about AC motors).

 

[MikeMl]

Thanks guys.
I'm not to design by myself an housing wiring, but rather want to understand how the existing housing wiring handles high starting current above 16A.



So if an wall outlet is 16Arms rated, it could still handle a starting current of say 22A?
(Yes, i'm talking about AC motors).

Yes and lots more. For example, the capacitor-start induction motor in my table saw draws ~10A when running, but probably draws 4 to 5 times that much during starting. I have started it hundreds of times without smoking anything... Same in my freefer, freezer, heating system blower motor, etc, etc. I don't know the spec for residential wiring, but residential circuit-breakers are able to support an in-rush of several times what is stamped on the handle. They are thermal breakers, so they will supply a very-large current for a very-short time, or ~125% of rated current for several minutes...

 

[smanches]

smanches to think of the reason why the wire length doesn't effect the current they figure the thickness of wire for the wire based on power dissipation over a small length of wire. If that power dissipation is too high the wire will melt, if it's in the right range it'll just heat slightly, how long the wire doesn't matter, though the increased overall power dissipation will cause the voltage to drop. The amperage ratings for housing wiring are based on standard home construction methods to keep heating in the walls from getting too high.

I guess I was thinking of constant voltage at the appliance, which would make wire length a factor. Although voltage is only constant at the source, and falls off as it gets distributed, as you said. Current can stay the same as wire resistance increases due to the voltage falling. I guess I just inherently think of current falling when resistance goes up, since when you're engineering circuits, it's the current you are usually worried about more.

 

[alphacat]

Thank you very much for helping out.

Happy new year to you guys

 

[Boncuk]

I had a problem with a router rated 230VAC/1,500W.

It ran at 22,000rpm and caused the 16A automatic circuit breakers to trip off even with a low weight tool attached to it.

An extension cable of 1.5 square mm and 10m length solved the problem. The motor started normally and nothing got hot.

I guess the motor starting current was way too high for a 16A circuit breaker although it can easily handle 1,500W.

Boncuk

 

[Sceadwian]

Yeah a high speed device like that would present some problems, the starting current on that thing was probably insane. That's what motor starters are for. They can be as simple as a large value capacitor inline, but they're expensive and a failure point. The extension cord you used probably provided enough bulk resistance to lower the starting current, I'm sure it heated up impressively but only during the time it takes to start the rotor moving, which was a few ms. The only thing you'd have to worry about is if you somehow managed to lock the rotor and started it, but even basic common sense tells you you don't start a router while it's touching the workpiece =)