Fuse selection

[Shaneyj]

We're getting a new plasma table at my shop.
480V.
The manufacturer has stated 110A time delay fuses.
I found a 3 pole disco (200A) and in its specs it says "fuse class provision" is class H.
Does this mean it will only accept class h fuses?
Do I need to determine fuse type first, then spec disco based on that?
The manufacturer is of no help in specifying a fuse type.
Thanks for any input.

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[Jraef]

Fuse class should be specified by the plasma cutter supplier in their data sheets. It generally has to do with the level of protection THEIR equipment requires. Then once you know the fuse class, you have to ensure that the switch has the right clips in it.

http://www.elliottelectric.com/Stat...ricalTables/UL_Fuse_classification_chart.aspx

That said, Class H is a fuse type that is generally not used now. Originally they were "renewable" fuses, but later a non-renewable version was released once renewable fuses became reviled for their tendency to allow equipment damage since they required routine maintenance that never took place. But the other issue still existing is that Class H non-renewable fuses are only rated for 10kAIC and outside of residential installations, that's way too low now. Most reputable disconnect switch mfrs offer retrofit kits to change the clips to accept Class K or better yet, RK class fuses (the R means Rejection type, so that you can't plug in a lower level of fuse).

 

[petersonra]

We're getting a new plasma table at my shop.
480V.
The manufacturer has stated 110A time delay fuses.
I found a 3 pole disco (200A) and in its specs it says "fuse class provision" is class H.
Does this mean it will only accept class h fuses?
Do I need to determine fuse type first, then spec disco based on that?
The manufacturer is of no help in specifying a fuse type.
Thanks for any input.

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It sounds like they don't care as long as the fuses are time delay.

I would suggest using class J fuses unless the manufacturer says otherwise.That way you don't end up using oddball stuff that is hard to come by and you lose a day or two of production trying to come up with spares.

 

[Shaneyj]

Fuse class should be specified by the plasma cutter supplier in their data sheets. It generally has to do with the level of protection THEIR equipment requires. Then once you know the fuse class, you have to ensure that the switch has the right clips in it.

http://www.elliottelectric.com/Stat...ricalTables/UL_Fuse_classification_chart.aspx

That said, Class H is a fuse type that is generally not used now. Originally they were "renewable" fuses, but later a non-renewable version was released once renewable fuses became reviled for their tendency to allow equipment damage since they required routine maintenance that never took place. But the other issue still existing is that Class H non-renewable fuses are only rated for 10kAIC and outside of residential installations, that's way too low now. Most reputable disconnect switch mfrs offer retrofit kits to change the clips to accept Class K or better yet, RK class fuses (the R means Rejection type, so that you can't plug in a lower level of fuse).

Good info. Thank you

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[Shaneyj]

It sounds like they don't care as long as the fuses are time delay.

I would suggest using class J fuses unless the manufacturer says otherwise.That way you don't end up using oddball stuff that is hard to come by and you lose a day or two of production trying to come up with spares.

Not caring is an understatement... Not knowing may be accurate too.
I got on the phone with their tech department.
"do you specify a particular fuse"
"what do you mean?"
"The local rep came out and said 110A time delay fuses, but that was all the info he gave me. So do you require a particular class or type? "
"it depends on where you're at. Some places the code doesn't allow you to use a time delay fuse and you have to use a breaker."
I quit asking for info after that.
Not saying that isn't accurate, although I've never heard of it, but tech support wasn't much support.

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[Shaneyj]

It sounds like they don't care as long as the fuses are time delay.

I would suggest using class J fuses unless the manufacturer says otherwise.That way you don't end up using oddball stuff that is hard to come by and you lose a day or two of production trying to come up with spares.

Thanks for the advice btw. I'll go with something readily available

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[petersonra]

Personally, I can't imagine they would care whether you put in fuses or a CB for the branch circuit protection. It just should not make all that much difference and the BC protection is not supposed to be there to protect the device. It is there to protect the conductors.

if they "need" fuses to protect their device it should be part of the device.

 

[Shaneyj]

More information...
At 480v, rated input current is 86A. The rep, not the manufacturer, suggested a 110A fuse.
I'd like to use the panel nearest the selected location. About 40' away. Problem is this is panel is a Siemens type bqd and will only accept up to a 100A breaker.
Other option is to use main distribution panel, about 270' away. Obviously this increases cost of material.
Can you see a reason to use a 110A fuse over a 100A fuse in light of the fact that the cut sheet specifies 86A at 480V?

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[Jraef]

Personally, I can't imagine they would care whether you put in fuses or a CB for the branch circuit protection. It just should not make all that much difference and the BC protection is not supposed to be there to protect the device. It is there to protect the conductors.

if they "need" fuses to protect their device it should be part of the device.

With the device needing 480V, it would need to show an SCCR, and that is generally dependent on the fuse selection. Some OEMs will not include them, they will just tell the installer it is necessary.

I agree with the Class J though, fast acting is a good thing if there are any electronics ahead of the transformer. But if all of the electronics are down stream of the transformer, a Class RK5 would be my other suggestion simply because they are cheaper than Class J for the most part. In fact since that they don't seem to care it might indicate that the transformer is first in the circuit, so SCCR down stream of it is irrelevant and all it needs is any time delay fuse ahead of it.

 

[petersonra]

With the device needing 480V, it would need to show an SCCR, and that is generally dependent on the fuse selection. Some OEMs will not include them, they will just tell the installer it is necessary.

I agree with the Class J though, fast acting is a good thing if there are any electronics ahead of the transformer. But if all of the electronics are down stream of the transformer, a Class RK5 would be my other suggestion simply because they are cheaper than Class J for the most part. In fact since that they don't seem to care it might indicate that the transformer is first in the circuit, so SCCR down stream of it is irrelevant and all it needs is any time delay fuse ahead of it.

The OP said the manufacturer wanted time delay fuses though.

Normally the device would need to be marked with both the SCCR and any external fuses that might be needed to meet that SCCR. Depending on how the thing is listed, and to what standard, the marking might amount to something in the instruction manual.

I don't recall there is any requirement to mark the SCCR of a plasma cutter though.

 

[Shaneyj]

The OP said the manufacturer wanted time delay fuses though.

Normally the device would need to be marked with both the SCCR and any external fuses that might be needed to meet that SCCR. Depending on how the thing is listed, and to what standard, the marking might amount to something in the instruction manual.

I don't recall there is any requirement to mark the SCCR of a plasma cutter though.

To be clear the piece of information about the time delay fuse came from the dealer. It was a sales guy they didn't have any answers for my questions.
When I got on the phone with the actual manufacturer, hypertherm, their technical support told me they don't specify overcurrent protection.
The only information they give is rated current at various voltages.

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[petersonra]

To be clear the piece of information about the time delay fuse came from the dealer. It was a sales guy they didn't have any answers for my questions.
When I got on the phone with the actual manufacturer, hypertherm, their technical support told me they don't specify overcurrent protection.
The only information they give is rated current at various voltages.

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I would select the next standard sized CB that is 125% over the rated current of the device.

what PN did you buy? that way we can look at the manual and see what it actually says. These are European so my guess is they don't have a meaningful SCCR.

 

[Shaneyj]

I would select the next standard sized CB that is 125% over the rated current of the device.

what PN did you buy? that way we can look at the manual and see what it actually says. These are European so my guess is they don't have a meaningful SCCR.

It's a hypertherm xpr 300.
63kW
86A at 480V
71.4kVA

Why 125%? Just to be safe? Our current plasma table does not run more than 20-30 minutes at a time. I don't suspect the new table to be any more than that either.

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[petersonra]

It's a hypertherm xpr 300.
63kW
86A at 480V
71.4kVA

Why 125%? Just to be safe? Our current plasma table does not run more than 20-30 minutes at a time. I don't suspect the new table to be any more than that either.

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I would want to take no chances of tripping the breaker or fuse. It is cheap to make the wires and ocpd rating a little more than the bare minimum it might need to be but if you have to run new wires and change out the overcurrent protection device later on because it trips now and then you won't have saved any money.

 

[petersonra]

I took a look at the manual.


86 x 125% = 108 Amps so the 110 Amp fuse they recommend is the same I would have chosen anyway.

I don't know if this means you have to have fuses or if you can use a CB. It reads a lot like the gibberish found in many CNC manuals.

Circuit breaker and fuse requirements
For main feed protection, choose a circuit breaker or fuse that is large enough to withstand all
branch-feed loads for both inrush and steady-state current. See Table 6 on page 39 for the
recommended time-delay fuse sizes.
You must choose time-delay fuses and circuit breakers that can withstand inrush current that is up
to 15 times the rated input current for 0.01 seconds and up to 10 times the rated input current for
0.1 seconds.
The size requirements for breakers or fuses at your site can change because of the following:
 Local line conditions (such as source and line impedance and voltage fluctuations)
 Product inrush characteristics
 Regulatory requirements
Contact a licensed electrician for more information about the codes in your location.
 The plasma power supply has a factory-installed inrush resistor. If
time-delay, high-inrush fuses are not permitted at your site because of
national or local codes, use a motor-start circuit breaker or equivalent.

I don't think motor protection CBs are listed for branch circuit protection.

I don't see a SCCR either.

Someone should ask them what the SCCR is. It clearly has an industrial control panel that is part of it and it would appear to meet the definition of an industrial machine so it requires a SCCR.

 

[Shaneyj]

I took a look at the manual.


86 x 125% = 108 Amps so the 110 Amp fuse they recommend is the same I would have chosen anyway.

I don't know if this means you have to have fuses or if you can use a CB. It reads a lot like the gibberish found in many CNC manuals.


I don't think motor protection CBs are listed for branch circuit protection.

I don't see a SCCR either.

Someone should ask them what the SCCR is. It clearly has an industrial control panel that is part of it and it would appear to meet the definition of an industrial machine so it requires a SCCR.

Thank you for the input...
Does the sccr have to be labeled on the control panel?
If so, I'll wait another week until the equipment is on site.

Fuse aic needs to be higher than panel sccr? Or is fuse selection based on available fault current at disconnect?
Thanks for clarity


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[petersonra]

Thank you for the input...
Does the sccr have to be labeled on the control panel?
If so, I'll wait another week until the equipment is on site.

Fuse aic needs to be higher than panel sccr? Or is fuse selection based on available fault current at disconnect?
Thanks for clarity


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Both OCPD AIC rating and the SCCR of the control panel have to exceed the available short circuit rating at the OCPD and control panel, respectively.

If you use class J fuses or class RK5 fuses chances are you will not have an issue because they have very high AIC ratings.

The code requires industrial control panels be marked with the SCCR.

409.22 Short-Circuit Current Rating.
(A) Installation. An industrial control panel shall not be
installed where the available short-circuit current exceeds its
short-circuit current rating as marked in accordance with 409.110(4).

409.110 Marking. An industrial control panel shall be marked
with the following information that is plainly visible after installation:
...
4) Short-circuit current rating of the industrial control panel
based on one of the following:
a. Short-circuit current rating of a listed and labeled
assembly
b. Short-circuit current rating established utilizing an
approved method

It does not say who has to do the marking. Just requires the marking. Usually it is a nameplate on the door of the control panel because article 670 requires an actual nameplate for industrial machinery, so you kill two birds with one stone, so to speak.

670.3 Machine Nameplate Data.
Informational Note: See 430.22(E) and 430.26 for duty cycle
requirements.
(A) Permanent Nameplate. A permanent nameplate shall be
attached to the control equipment enclosure or machine and
shall be plainly visible after installation. The nameplate shall
include the following information:
...
(4) Short-circuit current rating of the machine industrial
control panel based on one of the following:
a. Short-circuit current rating of a listed and labeled
machine control enclosure or assembly
b. Short-circuit current rating established utilizing an
approved method

Again there is no requirement that this nameplate be affixed by the manufacturer. Just that it be present.

 

[kwired]

Doesn't plasma cutters fall under the scope of art 630 and you would size conductors and overcurrent protection according to that article?

 

[Shaneyj]

Doesn't plasma cutters fall under the scope of art 630 and you would size conductors and overcurrent protection according to that article?

You're right.
630.1

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[petersonra]

Doesn't plasma cutters fall under the scope of art 630 and you would size conductors and overcurrent protection according to that article?

630.1 Scope. This article covers apparatus for electric arc
welding, resistance welding,

plasma cutting,

and other similar
welding and cutting process equipment that is connected to an
electrical supply system.
630.6 Listing. All welding and cutting power equipment
under the scope of this article shall be listed.

I don't think this equipment is listed.

Interestingly, there are a fair number of special requirements in this section for welders but I did not see any special requirements for plasma cutters.

Part II only applies to arc welders. Part III only to resistance welders. Part IV only to welding cables.

So it would appear to me that the only special requirement found in article 630 that applies to plasma cutters is the requirement that they be listed found in part I, that is new to 2017.

If something is covered in article 630 does that exempt them from other 6XX articles? I don't see how it exempts them from the control panel requirements found in article 4XX.