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teeg123

Member
Location
Maine
Occupation
Journeyman Electrician
I have a question on a practice exam and have not been able to grasp it.
The disconnecting means for a 50 HP, three-phase, 460 V induction motor shall have a minimum ampere rating of ?

1/ 60amps
2/ 100 amps
3/ 125 amps

So im in the 2023 nec I go to table 430.250 find my FLC of 65 amps
65amps X 1.15=74.75
for some reason be it a brain crap or what I cant seem to the answer they want of 100 amps
table 430.52 does my no good. I feel like im just missing something silly and will kick myself in the arse for it. The induction part appears to my to be the thing im messing up.

thanks for any help or assistance
 
Well it can’t be 60. It could be either of the other 2 but only one of them is the minimum.

But I’m not sure that’s right.
 
the answer s given but no steps on how to achieve it. i do appreciate everyone's help.
 
Rob, yes 100 amps is the answer, but I don't imagine that they are rounding up to 110 from 74.75. I very well could be wrong.
 
teeg123 said:
Rob, yes 100 amps is the answer, but I don't imagine that they are rounding up to 110 from 74.75. I very well could be wrong.
Click to expand...
Well the short answer is 74.75 is greater than 60 amps so 1) cannot be the answer. You're then left with two choices 100 and 125 amps, both are greater than 74.75 so it could be either 100 or 125 amps. Since they've asked for the minimum size and since either 100 or 125 would be code compliant the minimum would be the smaller of the two or 100 amps.
 
I had this question, on the state test and wasn't sure of the correct answer
4 branch circuit run to a remote sign, 2 30amp and 2 20amp what is the minimum size grounding?
So do I add them together making it 100 amps making it a #8 Awg.
or do you use a single 30 amp???
thanks in advance.
 
another question,
what are acceptable grounding method for a remote sign? 2 8foot ground rods, the bolts encased in the concrete, rmc with grounding bushing or not needed because its a sign
article 250.52 concrete encased needs to be 20 ft so bolts won't work
ground rods (possible)
My opinion was the rmc?

thanks
 
teeg123 said:
I had this question, on the state test and wasn't sure of the correct answer
4 branch circuit run to a remote sign, 2 30amp and 2 20amp what is the minimum size grounding?
So do I add them together making it 100 amps making it a #8 Awg.
or do you use a single 30 amp???
thanks in advance.
Click to expand...
If there in the same raceway. A.single EGC would be required based on the largest over current device (30 amp). With out more info #10 would be your answer. 250.122
 
teeg123 said:
another question,
what are acceptable grounding method for a remote sign? 2 8foot ground rods, the bolts encased in the concrete, rmc with grounding bushing or not needed because its a sign
article 250.52 concrete encased needs to be 20 ft so bolts won't work
ground rods (possible)
My opinion was the rmc?

thanks
Click to expand...
The qualifed EGC. 250.118.
 
1. Nobody makes 75a disconnects, so the minimum available.

2. No electrodes required (unless there's a panel at the sign.)
 
Tulsa Electrician said:
If there in the same raceway. A.single EGC would be required based on the largest over current device (30 amp). With out more info #10 would be your answer. 250.122
Click to expand...
i see that in 250.122(c) but where does it say to use the highest?
I see in 250.122(F)(1)(a) Single raceway to use table 250.122 but where do you find weather to use the highest or total ???

thanks very much
 
teeg123 said:
i see that in 250.122(c) but where does it say to use the highest?
Click to expand...
(C) Multiple Circuits.
A single equipment grounding conductor shall be permitted to be installed for multiple circuits that are installed in the same raceway, cable, trench, or cable tray. It shall be sized from Table 250.122 for the largest overcurrent device protecting circuit conductors in the raceway, cable, trench, or cable tray. Equipment grounding conductors instal⁠led in cable trays shall meet the minimum requirements of 392.10(B)(1)(c).
Click to expand...
 
teeg123 said:
the answer s given but no steps on how to achieve it. i do appreciate everyone's help.
Click to expand...
60 and 100 amps would be pretty standard switch ratings in NEMA equipment lines. Maybe 125amps as well. Funny thing is in the IEC world where SI (base 10) units are common they have standard electrical device ratings of 16, 32 and 63 amps.

When it comes to general purpose safety switches it jumps from 100 amps to 200 amps.

Just trying to give an idea where the potential answers might be coming from.
 
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