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NEC 2020 430.52(C)(1) exp no. 2

220 Views 14 Replies 4 Participants Last post by  MotoGP1199
I am not a motor installer or knowledgeable on motor controls very much. I'm looking over a practice test book for Masters and have heard about this code before 430.52(C)(1) exception no. 2. But I'm having trouble understanding it if the motor is hard to start why would lowering the OCPD be helpful. I'm thinking that if it's hard to start wouldn't you want more current for startup current???
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Is this what you’re talking about? I don’t see a decrease in there.

Exception No. 2:
Where the rating specified in Table 430.52, or the rating modified by Exception No. 1, is not sufficient for the starting current of the motor:

  • (1)
    The rating of a nontime-delay fuse not exceeding 600 amperes or a time-delay Class CC fuse shall be permitted to be increased but shall in no case exceed 400 percent of the full-load current.
  • (2)
    The rating of a time-delay (dual-element) fuse shall be permitted to be increased but shall in no case exceed 225 percent of the full-load current.
  • (3)
    The rating of an inverse time circuit breaker shall be permitted to be increased but shall in no case exceed 400 percent for full-load currents of 100 amperes or less or 300 percent for full-load currents greater than 100 amperes.
  • (4)
    The rating of a fuse of 601–6000 ampere classification shall be permitted to be increased but shall in no case exceed 300 percent of the full-load current.
 

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I am not a motor installer or knowledgeable on motor controls very much. I'm looking over a practice test book for Masters and have heard about this code before 430.52(C)(1) exception no. 2. But I'm having trouble understanding it if the motor is hard to start why would lowering the OCPD be helpful. I'm thinking that if it's hard to start wouldn't you want more current for startup current???
Are you reading the actual code book or a practice book?

Re read it From the actual code book. It says you can increase the size of OCPD, but can't exceed a certain number based on the type of overcurrent protection you are using.

Per 2020 nec:

Exception No. 2: Where the rating specified in Table 430.52, or the
rating modified by Exception No. 1, is not sufficient for the starting current of the motor:
(1 ) The rating ofa nontime-delay fuse not exceeding 600 amperes or a time-delay Class CC fuse shall be permitted to be increased but shall in no case exceed 400 percent of the full-load current.
(2) The rating of a time-delay (dual -element ) fuse shall be permitted
to be increased but shall in no case exceed 225 percent ofthe fullload current.
(3) The rating ofan inverse time circuit breaker shall be permitted to be increased but shall in no case exceed 400 percent for full-load currents of 100 amperes or less or 300 percent for full-load currents greater than 100 amperes. matic restarting of the motor can result in injury to persons.
430.44 Orderly Shutdown. If immediate automatic shutdown of a motor by a motor overload protective device(s) would introduce additional or increased hazard (s) to a person (s) and continued motor operation is necessary for safe shutdown of equipment or process,
a motor overload sensing device(s)
complying with Part III of this article shall be permitted to be connected to a supervised alarm instead of causing immediate interruption of the motor circuit, so that corrective action or an orderly shutdown can be initiated.
70-318
(4 ) The rating of a fuse of 601-6000 ampere classification shall be permitted to be increased but shall in no case exceed 300 percent ofthe full-load current. Informational Note: See Informative Annex D, Example D8, and Figure 430.1.
 

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Discussion Starter · #5 ·
Are you reading the actual code book or a practice book?

Re read it From the actual code book. It says you can increase the size of OCPD, but can't exceed a certain number based on the type of overcurrent protection you are using.

Per 2020 nec:

Exception No. 2: Where the rating specified in Table 430.52, or the
rating modified by Exception No. 1, is not sufficient for the starting current of the motor:
(1 ) The rating ofa nontime-delay fuse not exceeding 600 amperes or a time-delay Class CC fuse shall be permitted to be increased but shall in no case exceed 400 percent of the full-load current.
(2) The rating of a time-delay (dual -element ) fuse shall be permitted
to be increased but shall in no case exceed 225 percent ofthe fullload current.
(3) The rating ofan inverse time circuit breaker shall be permitted to be increased but shall in no case exceed 400 percent for full-load currents of 100 amperes or less or 300 percent for full-load currents greater than 100 amperes. matic restarting of the motor can result in injury to persons.
430.44 Orderly Shutdown. If immediate automatic shutdown of a motor by a motor overload protective device(s) would introduce additional or increased hazard (s) to a person (s) and continued motor operation is necessary for safe shutdown of equipment or process,
a motor overload sensing device(s)
complying with Part III of this article shall be permitted to be connected to a supervised alarm instead of causing immediate interruption of the motor circuit, so that corrective action or an orderly shutdown can be initiated.
70-318
(4 ) The rating of a fuse of 601-6000 ampere classification shall be permitted to be increased but shall in no case exceed 300 percent ofthe full-load current. Informational Note: See Informative Annex D, Example D8, and Figure 430.1.
[/QUOTE. We had written this in NEC class. I had put Roundup for exception number one and then round down for exception number two... And that is because it's hard to start not fully understanding what they mean by hard to start. I'm one of those guys that I like to understand why instead of just reading a code article without understanding it it's easier for me to understand the concept




Book Publication Font Paper Paper product
 

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"Hard to start" is probably not the language I would use.

Where the values of table 430.52 are not sufficient for start up you can use this exception.

In other words if you're OCPD is tripping on start up then you're allowed to use exception #2, if you do use it however you're not allowed to round up to the next standard breaker size as that would exceed the values permitted.
 

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I get it now. This is an exception rule. It's allowing you to go higher than normal levels in the table if the motor is having trouble starting. It then gives you a new maximum percent. If you multiply the motor FLA by that percent you can INCREASE your OCPD but can't use the next size up breaker rule. You have to stay under that new allowed overcurrent percent. Say you got a number of 105 amps after using that new higher percent that is above the table. You would have to use a 100 amp breaker and not go up to the next size larger breaker. It's still a larger breaker than what was allowed by the standard procedure.
 

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Discussion Starter · #11 ·
Everything says it shall be allowed to be Increased. You just can't exceed a certain percent. Where are you seeing round down?(except your hand writing)
I am not. I will scratch that off. I see something in the Masters practice book that says the next lower standard but I think this will clear it up because I wasn't sure why we wrote that or if I made a mistake
 

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Discussion Starter · #12 ·
I get it now. This is an exception rule. It's allowing you to go higher than normal levels in the table if the motor is having trouble starting. It then gives you a new maximum percent. If you multiply the motor FLA by that percent you can INCREASE your OCPD but can't use the next size up breaker rule. You have to stay under that new allowed overcurrent percent. Say you got a number of 105 amps after using that new higher percent that is above the table. You would have to use a 100 amp breaker and not go up to the next size larger breaker. It's still a larger breaker than what was allowed by the standard procedure.
Yeah and I'm just realizing too that breakers also have delays depending on which one so these percentages are kind of making sense that the instantaneous trip would be very high etc
 

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If you compare the table values to this exception. The exception has higher values for everything. You just can't exceed those values(or use the next higher OCPD).


Look at single phase motor with an inverse time breaker. Table says 250%, exception says 400% or 300% based on motor size.

Example 1:
Motor FLA: 20 amps
Table: 50amp breaker
Exception:80 amp breaker.

Example 2:
Motor FLA 23 amps
Table: 60 amp breaker (actual calculation 57.5 amps) next size breaker up is 60).
Exception: 90 amp breaker (actual calculation 92 amps) you can't exceed 400% so you go to the next size smaller breaker at 90 amps.

As you can see your still increasing the OCPD for starting your just not allowed to exceed the new value.
 

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Discussion Starter · #14 ·
If you compare the table values to this exception. The exception has higher values for everything. You just can't exceed those values(or use the next higher OCPD).


Look at single phase motor with an inverse time breaker. Table says 250%, exception says 400% or 300% based on motor size.

Example 1:
Motor FLA: 20 amps
Table: 50amp breaker
Exception:80 amp breaker.

Example 2:
Motor FLA 23 amps
Table: 60 amp breaker (actual calculation 57.5 amps) next size breaker up is 60).
Exception: 90 amp breaker (actual calculation 92 amps) you can't exceed 400% so you go to the next size smaller breaker at 90 amps.

As you can see you
If you compare the table values to this exception. The exception has higher values for everything. You just can't exceed those values(or use the next higher OCPD).


Look at single phase motor with an inverse time breaker. Table says 250%, exception says 400% or 300% based on motor size.

Example 1:
Motor FLA: 20 amps
Table: 50amp breaker
Exception:80 amp breaker.

Example 2:
Motor FLA 23 amps
Table: 60 amp breaker (actual calculation 57.5 amps) next size breaker up is 60).
Exception: 90 amp breaker (actual calculation 92 amps) you can't exceed 400% so you go to the next size smaller breaker at 90 amps.

As you can see your still increasing the OCPD for starting your just not allowed to exceed the new value.
Oh I think I realize why we said round down You do have to do the 400% like in your examples however if it's in between two breaker sizes you can use the lower one because you're already increasing it so much I think that's why we put that in there I don't see any language that says you can do that though that was my problem
 

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It says in the exception. "In no case shall you exceed" a certain value. That wording prohibits you for using the next size up rule.

If your not use to motors, it will also throw you for a loop as my examples would be allowed to be wired with #12 (example 1) or #10(example 2) copper thhn. Even with the 80 and 90 amp breakers. As this is only providing ground fault and short circuit protection. You would usually have some other sort of overload relay or heaters in the circuit.
 
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