Motor Overload Tripping.

[mdakxotaz]

Have what I feel is probably a stupid question and I think I know the answer already but here it goes. When measuring line to line in a 3-phase system, what you've got is what you've got?. What I mean by that is if I measure line to line and my multimeter reads 209V, is the system running 209V or with the three phases is it 480V?

I've got a motor which its nameplate reads the following.

Voltage :208 - 230/460
Amps :5.7 - 5.4/ 2.7

The overload is adjustable from 2.2A-3.4A, set at 2.8A, which even if this was running 460V, would be to low based on the 125% from 430.32(A)(1). With a clamp on ammeter around one leg reads 3.2A after the initial instantaneous current jump. The overload just started tripping today, this machine has been in the building for about a year now and never had this problem that I know of.

I'm fairly new here but it seems to me that this overload device is sized according to a 460V system, which would be incorrect in our application. For now I've turned the device up to its maximum 3.4A and haven't had it trip for the last few hours. Appreciate any feedback.

 

[jim dungar]

L-L is L-L no multipliers are needed.

Nominal voltage systems yield:
208Y/120V has 208V L-L and 120V L-N/G
480Y/277 V has 480V L-L and 277V L-N/G

When troubleshooting, I suggest you always measure all of the possible voltages (3) L-L, (3) L-N, (3) L-G, and (1) N-G

 

[ohmhead]

motor starter not correct size ?

motor starter not correct size ?

Well check your motor art 430 nec overloads 110 % to 115 % , wire size is 125% not the overloads but your starter size must be for your motor size in horse power meaning size 0 or size 00 nema sized and rated for horse power for your motor so i would say your starter is not the correct size or you can change out your contactor and overloads to match your motor . Also motors dont always run at what the nec code says in the tables you go by nameplate to size a motor . Best to ya

 

[augie47]

...........if I measure line to line and my multimeter reads 209V, is the system running 209V or with the three phases is it 480V?

I've got a motor which its nameplate reads the following.

Voltage :208 - 230/460
Amps :5.7 - 5.4/ 2.7

The overload is adjustable from 2.2A-3.4A, set at 2.8A, .....................
I'm fairly new here but it seems to me that this overload device is sized according to a 460V system, which would be incorrect in our application. For now I've turned the device up to its maximum 3.4A and haven't had it trip for the last few hours. Appreciate any feedback.

It does appear that you have a overload set for 480 and a motor operating at 208v. Normally you set your overload per nameplate data.
Check the starter and be sure it's rated for the hp of your motor. If so you can probably obatin another overload unit.

 

[mdakxotaz]

Well check your motor art 430 nec overloads 110 % to 115 % , wire size is 125% not the overloads

ohmhead, I looked but not sure where you found the 110%115%, if you look at 430.32(A)(1) it shows motors over 1 HP if marked with a temperature rise 40C or less, or SF 1.15 or greater size 125%, which in this case our motor is operating 2HP with SF 1.15.

If not marked it states "All other motors 115%"

Also, there is no HP rating on the contactor or overload device, only Voltage and Kw ratings. which this contactor does state it will support up to 550V

Thanks for the clarification jim, these are the kinds of things I've learned but when it comes time to use them they don't always come back full force .. makes good sense though. And sure enough when tested there is 118V L-N.

 

[ohmhead]

Well yes 2008 code book 125% all others 115% . Now back to starter its not the max voltage of the starter its the amps that its rated for thats important . But the starter must be for that horse power rating of that motor and voltage if you must change kw to horsepower do that to find size of starter . Best to ya

 

[RHJohnson]

Well yes 2008 code book 125% all others 115% . Now back to starter its not the max voltage of the starter its the amps that its rated for thats important .

Size 0 and 00 are large enough for the motor. If you measure 209vac phase to phase on all posibilities - and that is your correct supply voltage - then all you need do is install the correct heater (overload) size.
If it is one of those low end contactors with built in adjustable overload trip you will need to change it out to one with the correct trip range.
Edited post: You need to have an adjustable trip that will cover 5.7 amps - if you actually have 209vac supplied.