AC power

[Smart $]

...
As you can see from the nameplate rating, the unit draws much less current during normal running. If there is a ground fault, the CBer will pick it up.
...

While true for bolted faults and shorts, what protects the conductors from resistive faults and shorts, especially those that do not occur in a thermally and/or overload-protected motor-compressor.

 

[e57]

240.4 allowing you to even consider looking at 440 says,
I'd say B & D are still requirements, and not specifically over-ridden in 440.

I was rushed to dinner when I typed this one...
I'm retracting "B"... But I still think D still applies... B is over-ridden in a few places.... :roll: But as mention IMO "D" is only over-ridden in one...

e57
What you may not understand about the nameplate rating of A/C.
The manufacturer has already performed the calculations. The reason for the higher OCPD is the provide relief from the CBer tripping during startup/inrush. (very similar to motors - which an A/C unit has)
As you can see from the nameplate rating, the unit draws much less current during normal running. If there is a ground fault, the CBer will pick it up.

240.(D) is not applicable, and that is stated in the first paragraph of 240.4, which goes on to allow 240.4(G) as the section we reference.

The manufacturer is only required to do the calcs on hermetic units with a nameplate - the others are handled differently, and may even be field fabricated units or components lacking nameplate ratings in combination with other components, depending on how they are built and controlled. In your example about motors - many instances would increase conductor size rather than allow a reduction...

And 440 ONLY applies IF the AC, or refer is hermetic or contains a hermetic component - not all of them are...

[QUOTE='02 handbook]Article 440 provides special considerations necessary for circuits supplying hermetic refrigerant motor-compressors and is in addition to or amendatory of the provisions of Article 430 and other applicable articles. However, many requirements, such as disconnecting means, controllers, single or group installations, and sizing of conductors, are the same as or similar to those applied in Article 430.
Article 440 does not apply unless a hermetic refrigerant motor-compressor is supplied. Article 440 must be applied in conjunction with Article 430.
Note the terms rated-load current and branch-circuit selection current, defined in 440.2. When a branch-circuit selection current is marked on a nameplate, it must be used instead of the rated-load current to determine the size of the disconnecting means, the controller, the motor branch-circuit conductors, and the overcurrent protective devices for the branch-circuit conductors and the motor. The value of branch-circuit selection current will always be greater than the marked rated-load current. [/QUOTE]
There are a few things in motors that get you out of 240.4(D) but not many. And like wise much of 440 also required increases in branch conductor size (by requiring a higher ampacity rating) except for a few. While the ampacity rating of the branch circuit may go up, or down - I don't think the purpose of 240.4(D) should be ignored... "Unless specifically permitted" - there are cases where it is "specifically permitted" but not under a blanket of permission...

 

[Power Tech]

So, what is the practical thing to do? As a standard practice, I follow the maximum CB on the A/C nameplate to size the wire and circuit. I don't want call backs. What should be an industry standard? I don't want to overbuild unnecessarily.

On other motor loads: One time fuses - FLA X 300%
Time delay - 125%

 

[hillbilly]

So, what is the practical thing to do? As a standard practice, I follow the maximum CB on the A/C nameplate to size the wire and circuit. I don't want call backs. What should be an industry standard? I don't want to overbuild unnecessarily.

On other motor loads: One time fuses - FLA X 300%
Time delay - 125%

For packaged, Hermetic, Heat/AC units.

The practical thing is ..... to do as the code allows and size the conductors per the nameplate minimum ampacity and size the Breaker (or fuses) per the maximum ampacity.

If a unit calls for a minimum 28 amp circuit, that means a circuit that's capable of delivering 28 amps at the nameplate (+-) voltage.
This may require you to do some math, and look at factors such as voltage drop, etc... ....same as any other circuit.
This may require you to increase the conductor size, but (IMO) would be the only reason to do so.

That is (in my opinion) the industry standard.

If you're sizing the conductors per the maximum allowed breaker (or fuses)....IMO...you are overbuilding....and spending a lot of un-necessary$$$.

It really is that simple.

Just my opinion
steve

 

[don_resqcapt19]

...
And 440 ONLY applies IF the AC, or refer is hermetic or contains a hermetic component - not all of them are...

I never seen a newly installed non-hermetic AC compressor. I have worked on some previously installed ones, but never a new one.

There are a few things in motors that get you out of 240.4(D) but not many. And like wise much of 440 also required increases in branch conductor size (by requiring a higher ampacity rating) except for a few. While the ampacity rating of the branch circuit may go up, or down - I don't think the purpose of 240.4(D) should be ignored... "Unless specifically permitted" - there are cases where it is "specifically permitted" but not under a blanket of permission...

What is the purpose of 240.4(D)? I am not aware of any real purpose or technical substantiation for that section. It is still my reading of the code that the only overcurrent protection rules that apply to conductors installed under the scope of Article 440 are found in that article.

 

[iwire]

I never seen a newly installed non-hermetic AC compressor. I have worked on some previously installed ones, but never a new one.

We still install non-hermetic refrigeration compressors. Some for cold storage warehouse are large 150 - 200 HP, but BJs wholesale club uses them at their stores in smaller sizes like 5 to 25 HP.

 

[Chamuit]

Sounds like this would make a great poll question, sans explanations.

I'd put #8 NM and breaker at 40 amps.

240.4.D is where I would work from, and you couldn't change my mind. I don't think. Because using "ROMEX" is the key here.

28.5 MCA ? .8 = 35.625A

 

[don_resqcapt19]

We still install non-hermetic refrigeration compressors. Some for cold storage warehouse are large 150 - 200 HP, but BJs wholesale club uses them at their stores in smaller sizes like 5 to 25 HP.

I have been out of the commercial area for a long time and I shouldn't make comments about things like that.

 

[don_resqcapt19]

Sounds like this would make a great poll question, sans explanations.

I'd put #8 NM and breaker at 40 amps.

240.4.D is where I would work from, and you couldn't change my mind. I don't think. Because using "ROMEX" is the key here.

28.5 MCA ? .8 = 35.625A

The ".8" factor is already built into the MCA. No need to do it again.

 

[e57]

What is the purpose of 240.4(D)? I am not aware of any real purpose or technical substantiation for that section.

My understanding of it - is to recongize the short-circuit and over-load clearing limitations of fuses and CB's. Which can often be far in excess of the currents listed in the tables of 310.15 that were provided for calculation purposes.

I'm gleaning that from the comments in the 08 change comments:
http://www.nfpa.org/assets/files/PDF/ROP/NEC2008ROP.pdf
From the writer of that proposal - obvious a promotion of product...
http://www.cooperbussmann.com/pdf/450ac4c6-b7d7-46c7-9f6b-b9b70f2463d7.pdf

I believe it was put in the code in 1999 - and I cant get the rop's and roc's for it.... (Anyone?)

 

[e57]

We still install non-hermetic refrigeration compressors. Some for cold storage warehouse are large 150 - 200 HP, but BJs wholesale club uses them at their stores in smaller sizes like 5 to 25 HP.

And some of the smaller company brand manufacturers of AC units - most have gone to hermetic - but not all. Hermetic is not servicable - just replacable in some instances....

 

[e57]

Re:240.4(D)

I believe it was put in the code in 1999 - and I cant get the rop's and roc's for it.... (Anyone?)

Further looking into it - the wording was put into 240 from a note at the bottom of the 310.16, and 310.17 tables that are based off of the Neher-McGrath equation developed in the late 50's for the calculation of underground duct work, and apparently 'someone', 'sometime' felt that these conductors were to small to work well with this particular formula and futher limit them...

 

[don_resqcapt19]

My understanding of it - is to recongize the short-circuit and over-load clearing limitations of fuses and CB's. Which can often be far in excess of the currents listed in the tables of 310.15 that were provided for calculation purposes.

I'm gleaning that from the comments in the 08 change comments:
http://www.nfpa.org/assets/files/PDF/ROP/NEC2008ROP.pdf
From the writer of that proposal - obvious a promotion of product...
http://www.cooperbussmann.com/pdf/450ac4c6-b7d7-46c7-9f6b-b9b70f2463d7.pdf

I believe it was put in the code in 1999 - and I cant get the rop's and roc's for it.... (Anyone?)

It has been in the code for a long time...it just changed locations in 99. I don't buy the short circuit and over-load clearing issues. Look at the safe current values for short times in the Bussmann document you linked to. A breaker of fuse will open quickly enough that the conductor won't be damaged.
PS: What proposal for the 2008 code are you talking about...the link is for the complete ROP.

 

[LarryFine]

Not just one, but any that apply simultaneously to the installation. Yes it could be just one, but there is nothing which states only one shall apply... and as we are discussing, it is possible, as it seems to me, that two can apply.

Absolutely. I was just pointing out that any one (yes, or more) can apply, or rather, be applied.

 

[LarryFine]

I don't want to overbuild unnecessarily.

For packaged, Hermetic, Heat/AC units.

If you're sizing the conductors per the maximum allowed breaker (or fuses)....IMO...you are overbuilding....and spending a lot of un-necessary$$$.

It really is that simple.

Agreed on all points.

 

[e57]

It has been in the code for a long time...it just changed locations in 99. I don't buy the short circuit and over-load clearing issues. Look at the safe current values for short times in the Bussmann document you linked to. A breaker of fuse will open quickly enough that the conductor won't be damaged.

PS: What proposal for the 2008 code are you talking about...the link is for the complete ROP.

I was looking for 240.4(D)'s purpose and statements about it. Why were conductors #22~#10 limited additionally in the first place? (Specifically, #14-10 with OCP values 15A ~ 30A) Since it has been in the code for some time, maybe the proposal to move it to 240 from the tables in 310 may have mentioned its purpose?

The '08 change of 240'4(D) (sponsored by Bussman) is the one allows use of the of Bussman products for the application - go figure. And Bussman’s justifications for the change was to say in so many words – ‘Ooo we have a product that can over-come these issues… And that there are flaws in the formula being used by other industry associations…’ (ones that create the values on the tables)

Looking further into how the tables were created and other very lengthy discussions in public over the decades of stuff on the internet – much of it way too lengthy or not even available for cut and paste is – that the formula was never really suited to small conductors in most situations. (A few criticized use of the formula above ground – in attic or direct sunlight…) Which I assume to be true – since from my personal experience, if you loaded sizes #14~#10 to the values in the tables continuously – you would have a pretty hot conductor. The ones you normally see insulation damage on…. I’m sure others would agree that 25A on #14, 30A on #12, and 40A on #10 (24-7 for years) won’t hold up very well.

Anyway I guess I’ve side tracked on this enough – and surely it will come up again. Since no one seems to know the purpose of 240.4(D), and you and I have debated whether or not 240.4(G) gets you out of the rest of 240.4 and will continue to disagree on it, which is the main question IMO. ( ‘till next time… )

 

[Minuteman]

Sounds to me like one of you should introduce clarification language on this for the next code cycle.

 

[e57]

Sounds to me like one of you should introduce clarification language on this for the next code cycle.

I think you're right - but it'll have to be the next code cycle after...

 

[Minuteman]

I think you're right - but it'll have to be the next code cycle after...

2014 or 2017?

 

[Skokian]

He may have you on this one...



28.5A ? 115% = 32.8A

Also, for other motors, you man need to multiply by 1.25 (125%) per Article 430 (430.22, for example).

Regards . . .

Jim