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Does my Control Panel require "Main" fuses after my disconnect?
3

Does my Control Panel require "Main" fuses after my disconnect?

Does my Control Panel require "Main" fuses after my disconnect?

(OP)
Hi,

I am designing a control panel for machine control. I will be including a disconnect to which a supply power circuit (208 VAC 3 phase 80 amps) will be wired to. When the disconnect is turned on, 208 VAC will be distributed to the following components:
  1. transformer (208 VAC to 120 VAC)
  2. two variable frequency drives
  3. three solid state power controllers for resistance heaters
  4. one 24 VDC power supply
I am going to include dedicated branch fuses for all of the above components. What I am unsure of is whether I should also include "Main" 80 amp fuses between the disconnect and my branch fuses. If anyone here can offer an opinion as to whether "Main" 80 amp fuses are recommended (either for code or other reasons), or if they are unnecessary, I would greatly appreciate it. This particular panel will be used in the United States, but I also like to comply with european (CE) and Canadian guidelines as much as I can.

Thanks in advance,
Paul






RE: Does my Control Panel require "Main" fuses after my disconnect?

dear Mr. PaulKraemer (Electrical)(OP)23 Dec 22 19:38
" #1....I am designing a control panel for machine control. I will be including a disconnect to which a supply power circuit (208 VAC 3 phase 80 amps) will be wired to. When the disconnect is turned on, 208 VAC will be distributed to the following components:.......I am going to include dedicated branch fuses for all of the above components. What I am unsure of is whether I should also include "Main" 80 amp fuses between the disconnect and my branch fuses.....".
1. I assumed that (i) the disconnect is [NOT a circuit breaker].
BTW: A lockable CB can be used and is acceptable as a disconnect. A disconnect, does NOT open on SC or overload.
(ii) that the dedicated branch fuses (including the conductors) are rated for the load of individual components. Therefore, there will be numerous short lengths of conductors sized < 80A; connecting between the disconnect and the individual fuses.
1.1. Now consider: (i) how the up-stream conductor to the 80A disconnect is protected, and (ii) how the short lengths of much smaller conductors connecting to the individual fuses are protected by the up-stream protective device (Fuse or CB).

"#2....This particular panel will be used in the United States, but I also like to comply with european (CE) and Canadian guidelines as much as I can...."
2. (a)_ In the US and Canada , the NEC is the Law.
(b) In Europe, IEC applies. That has nothing to do with CE marking.
2.1 BTW: NEC and IEC standards are poles apart. They DO NOT see eye-to- eye in requirements and practices; except that "safety" is common.
Che Kuan Yau (Singapore)

RE: Does my Control Panel require "Main" fuses after my disconnect?

(OP)
Hi Che Kuan Yau,

Thank you for your response. The disconnect I had in mind is the Schneider Electric VCF4, as described in the link below...

https://www.se.com/ww/en/product/VCF4/tesys-vario-...

... I like that this is side-mount disconnect because I feel like it allows me to make better use of the space inside my panel than if I were to use a front (door) mounted disconnect. The VCF4 is not a circuit breaker, and it is not fusible - so if I want to add "Main" fuses, I'd have to purchase and find space for suitable fuse-holders that are separate from the disconnect. You are correct that I will be sizing my dedicated branch fuses for the load of the individual components they are dedicated for. I didn't mention it in my original post, but I am planning to put a distribution block between the disconnect and the branch fuses. With this being the case, I would have wires rated for 80 amps going from the disconnect to the distribution block. Then I would have smaller wires going from the distribution block to the branch fuses.

My up-stream conductions to the 80 amp disconnect will be protected by an 80 amp circuit breaker (provided by the facility in which the machine is installed). What I am trying to decide is whether there is a reason I should also include 80 amp fuses between the disconnect and the distribution block.

Regarding NEC vs IEC, I'd like to choose components that comply with both (if at all possible). In trying to see if this is possible, I found out that while the VCF4 disconnect I have in mind is rated for 80 amps per IEC, it might only be rated for 63 amps per UL. I am not sure exactly how UL relates to NEC, but I would like to comply with as many of these competing standards as I possibly can. With this being the case, I might try to find a different disconnect that is rated for 80 amps per IEC, NEC, and UL.

Any advice or suggestions you might have will be greatly appreciated.

Thanks again,
Paul

RE: Does my Control Panel require "Main" fuses after my disconnect?

If you are trying to make this a "universal" product intended for multiple installations in various parts of the world, can you guarantee that every customer will have, or install, the correct upstream circuit-protection?

My observation - and it is only that - has been that (rightly or wrongly) IEC wants circuit-breakers everywhere, and CSA wants fuses everywhere. I've seen many a European-sourced machine that needed the circuit-breakers removed and exchanged for fuses in order to get Electrical Safety Authority approval. You may wish to protect space in your panel for either a fuse-holder or the appropriate circuit-breakers, and simply omit them in the case that a particular end-user doesn't need it.

The disconnect switch that you linked to indicates certifications by IEC, UL, and CSA (among others) so that won't be a problem.

RE: Does my Control Panel require "Main" fuses after my disconnect?

Dear Mr. PaulKraemer
#1. "....The disconnect I had in mind is the Schneider Electric VCF4..."
Per data sheet: Check, (a) it is rated for 15kW at 230...240V (AC3). You have two VFDs kW?. (b) Rated conditional SC current 10kA associated fuse 80A aM/gG. The SC level at disconnector < 10kA?

#2. ".... but I am planning to put a distribution block between the disconnect and the branch fuses. ..... I would have wires rated for 80 amps going from the disconnect to the distribution block. Then I would have smaller wires going from the distribution block to the branch fuses...."
Check (a) the NEC requirement which is the law in the US. These small conductors shall be as short as possible, with extra insulation, shall NOT be bundled with the other wiring ete... per IEC.

#3. "... up-stream conductions to the 80 amp disconnect will be protected by an 80 amp circuit breaker ....... What I am trying to decide is whether there is a reason I should also include 80 amp fuses between the disconnect and the distribution block...".
NO, it does not serve any purposes if the distribution block SC is rated > 10kA.

#4. " ....Regarding NEC vs IEC, I'd like to choose components that comply with both (if at all possible)....."
As I had posted earlier NEC and IEC do not see eye-to-eye in ratings/requirements/practice.
The data sheet reads operation current 57A AC23. BTW the terminology of (AC 23 in IEC) is NOT in the NEC, ANSI, UL? , CAS dictionary.

#5. ".... I am not sure exactly how UL relates to NEC, but I would like to comply with as many of these competing standards as I possibly can. With this being the case, I might try to find a different disconnect that is rated for 80 amps per IEC, NEC, and UL...."
The UL is a "component/device/equipment " testing station. The NEC is the Law in the US pertaining to installation safety. They are independent (not related) organizations.

#6. "... but I would like to comply with as many of these competing standards as I possibly can. ..."
In the US and Canada, you comply in full to NEC, which is the Law. All IEC rated components/device/equipments shall be re-tested for us in the US. The same item usually ended up with different (voltage, current, kW) ratings and usage etc...etc.
Che Kuan Yau (Singapore)



RE: Does my Control Panel require "Main" fuses after my disconnect?

(OP)
Hi Brian and Che Kuan Yau -

Thank you for your responses. My first installation of this control panel will be forgiving in terms of regulatory requirements because it is to be an upgrade for a machine located in the facility where I work (in New Jersey, USA). Here, I can be certain that upstream circuit protection will be correct. As I do have similar machines in various parts of the world, I would like to do my best to design this control panel in a way that would make it as easily adaptable to requirements in other places as I can. Brian's suggestion that I may wish to reserve space in my panel for either a fuse-holder or the appropriate circuit-breakers, and simply omit them in the case that a particular end-user doesn't need it makes a lot of sense..

Regarding Che Kuan Yau's points #1-#6, I'll start out with #1.

Where I had mentioned the disconnect I had in mind is the Schneider Electric VCF4, you pointed out (a) that this is rated for 15 kW at 230..240V (AC3). You asked the kW of my two VFD's. I'm not sure if it makes a difference, but I actually have one true VFD (that drives an AC motor). My second drive is actually a DC drive (that drives a DC motor). Both the AC motor and the DC motor are 1 HP (0.75 kW)

You also pointed out that (b) this disconnect has a rated conditional SC current of 10kA associated fuse 80A aM/gG. I'm not sure I understand your question "The SC level at disconnector < 10kA?". Does this mean that I have to make sure the inbound supply power circuit is protected in a way so that it will not be able to supply and more than 10 kA?

If you don't mind, I'll try to get a firm grasp on point #1 before I follow up on points #2-6.

I really appreciate your help!

Best regards,
Paul

RE: Does my Control Panel require "Main" fuses after my disconnect?

I don't believe that disconnect is suitable as the main disconnect in an industrial control panel as per the UL or CSA listing. It appears to be listed as a manual motor controller so it's likely able to be used as a manual start/stop for a motor if it's installed along with other components, probably an overload and a breaker or fusible. There will be some combination of parts it works with for that application.

Just because an item has a UL or CSA on it doesn't mean it's suitable for the purpose you want to use it for.

RE: Does my Control Panel require "Main" fuses after my disconnect?

(OP)
Hi Lionel -

Thank you for your response. Your point is well taken that just because an item's spec sheet claims UL or CSA certification doesn't mean it is suitable for my intended purpose.

I just looked through the specs on the VCF4 disconnect I had in mind. I see that it lists the product type as "Emergency stop switch disconnector". Looking at the other specs, it seems that it is rated to disconnect the maximum 80 amps that the control panel I am designing will draw (which I plan to ensure either by an upstream (outside of my panel) circuit breaker in the facility, or possibly with fuses inside my panel. (Making the determination as to whether or not to include these fuses in my panel or whether it is acceptable to rely on the upstream (facility) circuit breaker was the main purpose of my original post.

I don't see anything specific that tells me that this VVCF4 disconnect is not intended for use as the main disconnect in an industrial control panel. If you happen to know a rating or certification I can look for that would tell me that a component is intended for this type of use, I would greatly appreciate it. If you happen to know of such a rating in UL, CSA, and/or IEC, I'd really appreciate it.

Thanks again for your help,
Paul

RE: Does my Control Panel require "Main" fuses after my disconnect?

No, hope and prayers is not how you determine if it is suitable for that purpose.

You look up the UL file number on the UL Product IQ site and find the CCN code. The UL508A supplement SA will tell you what CCN codes can be used for what purpose.

In this case, that thing is not suitable as a main disconnect just as I suspected. The CCN is NLRV, SA says 'Products marked "Suitable as motor disconnect" and used as a motor disconnect must be installed on the load side of the a branch circuit protective device for the circuit in which the motor controller is located.'

Definitely not the main disconnect since the branch circuit protection has to be ahead of it. Also, it can only be used as a motor disconnect, which rules out any other controls like switching a VFD.

I suggest you spend some time learning UL508A if you want to build control panels.

RE: Does my Control Panel require "Main" fuses after my disconnect?

(OP)
Thank you Lionel,

I definitely would like to study UL508A. Googling for this makes it appear that the ANSI webstore (https://webstore.ansi.org/) is probably the "official" place to get a copy of this (please correct me if I am wrong). The ANSI webstore makes it seem like the UL508A document is not available for a one-time purchase, but rather through a subscription that appears to be geared towards larger organizations with multiple users.

I am just one person with a desire to enhance my knowledge and a tight budget. If you (or anyone else here) might be able to suggest the most cost-effective way I might be able to obtain a copy of UL508A, I would greatly appreciate it.

Thanks again for your help.

Best regards,
Paul

RE: Does my Control Panel require "Main" fuses after my disconnect?

shopulstandards.com I think you can view it online for free there, but I haven't tried.

When the disconnect says it is 5kA when protected by J fuses it's a piece of crap. Any decent disconnect is at least 100kA when protected by J fuses.

RE: Does my Control Panel require "Main" fuses after my disconnect?

(OP)
Thank you Lionel,

The free digital viewer feature at shopulstandards.com works great! I'll take some time to read UL508A so I can be in a more informed position before following-up with more questions here.

I appreciate your help!

Best regards,
Paul

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