separating ac/dc inside a cabinet

[mobil1syn]

i have a customer who is pushing back on something i have not encountered before. the cabinet is a local control panel consisting of PL, PB, HMI, and two fiber converters. CL1, DIV2 with a purge. blue is 120v stuff, green 24v. everything on the left of the TBs are going to the door, everything on the right is coming from their homerun cables.

comments on submitted drawings were "AC/DC wires shall not run in the same duct. At least 2in spacing shall be maintained between AC & DC duct. Also show the 2" inside the Layout."

NEC says i can do it as long as insulation rating is good enough for highest voltage, nothing in ul508a, so what gives other than this is a preference? i have asked them to provide code to support their comment but nothing as of yet. as you can see space is at a premium, ive been shuffling things around to see if i can accommodate the request but cant come up with a solution. making the enclosure larger is not a feasible option.

is there a technical reason for the separation that i am missing?

 

[rupej]

The AC/DC separation thing isn't a code issue as far as I know but it is often used to combat noise on the DC bus. The 2" thing is a preference.


I'm rusty on this, but I believe IS wiring does require 2" spacing from non-IS wiring if you don't have it in a duct or some physical separation.

 

[VAN]

I think 120 is still fine per code (but I haven't kept up with it), its 240 and 480 that requires more protection.

However rule of thumb I always separate 120 and try covering it with some kind of shield to keep wondering hands out of it.

Can you move all 120 to the bottom and run it out under the panel and have 24 all run out the top?

Also, I'd push to get it out of a div2 area if you can. Not many reasons you can't run external and run wires in and seal the conduit.

edit - one thing we did with trays that absolutely had to mix 120 and 24 was run a flex conduit in the tray for the 24 and the 120 in the tray. BUT I don't recall if many electricians are OK with this approach. And as said, you get a noise problem what are you going to do, every support person will just say yeah... you ran it next to 120. Not my problem.

 

[willxfmr]

It's not a code issue, it's a customer spec. Most customers will never know if the panel is code compliant or not, but will refuse to pay if it does not meet their specs.

 

[James Mcquade]

willxfmr,
+1
it's a customer spec, build it to their spec or you ay not get aid until it does meet their specs.

 

[VAN]

willxfmr,
+1
it's a customer spec, build it to their spec or you ay not get aid until it does meet their specs.

You're a 100% wrong, never do what a customer asks that is illegal.

They can go **** themselves and find another panel builder that follows your logic.

I don't want to get sent to court for some ******* that thinks he knows what he wants.

 

[willxfmr]

You're a 100% wrong, never do what a customer asks that is illegal.

They can go **** themselves and find another panel builder that follows your logic.

I don't want to get sent to court for some ******* that thinks he knows what he wants.

There is nothing in the OP that would violate any code that I am aware of. If you see something there I missed, please enlighten me.



Bubba.

 

[Rson]

This is common practice in the automotive world. Maybe not the 2" - but definitely to have separate ductwork for 120V/24V.

Don't forget they also sell shielding separators for wire duct:

https://www.panduit.com/en/products...cessories/wiring-duct-accessories/sd4emi.html

Just in case trying to meet his spec causes your panel to explode in size - you might ask if that is acceptable.

There will almost always be a case where you need a 24V wire in an AC wire area. Especially when you are dealing with VFDs / Motor starters /etc.

 

[milldrone]

Speaking from the end user side

It's not a code issue, it's a customer spec.

willxfmr,
+1
.

This is common practice in the automotive world. Maybe not the 2" - but definitely to have separate ductwork for 120V/24V.

+ 2, my employer demands a 10 foot minimum red tape barrier when opening any cabinets with more than 50 volt potential. The best way to speed up the troubleshooting process is to use 24 volt controls and separate cabinets for the above 50 volt stuff. On often used over 50 volt cabinets we employ permanently mounted red tapes (like a bank would use to form waiting lines).

 

[mobil1syn]

thank you for the information guys

Also, I'd push to get it out of a div2 area if you can. Not many reasons you can't run external and run wires in and seal the conduit.

all of my work is C1, D2 so nothing special about this job. we are an industrial process OEM.

willxfmr,
+1
it's a customer spec, build it to their spec or you ay not get aid until it does meet their specs.

You're a 100% wrong, never do what a customer asks that is illegal.

They can go **** themselves and find another panel builder that follows your logic.

I don't want to get sent to court for some ******* that thinks he knows what he wants.

if the spec doesnt create a hazard then i have no issue accommodating it, if it is really outside the norm i will push back with schedule/commercial impacts. good way to test the waters on how much it matters to them.

in this case, the customer has been difficult from day 1, so im less inclined to be accommodating. for example, after plenty of back and forth on an FAT procedure for a bentley rack (which we bought, but is going into their panel), rev3 gets approval, do the FAT, they come back asking for a bunch of extra stuff not in the procedure. argue with them and ultimately they get half of what they want. have to have the TPI inspector come back, etc. what should of have been a 1 day deal has now consumed 4 days.

 

[Smeltz]

Just my thoughts, it's likely to do with the customers PPE requirements. If the DC is separated they can likely work on the panel without, or minimal, PPE. While not an issue for me now since I'm in a manufacturing plant, at the OEM machine builder I was previously these type of specs were becoming more and more prevalent. I never ran into any pushback. With some devices its impossible to not mix some AC and DC wiring.

 

[Jim3846]

If you UL sticker the panel that is a state by state inspector will usually just pass it when installed.
Your customer has put additional requirements on you as there in plant spec. There willing to pay additional for this so if does not vioiate NEC, UL, or local codes then why not do it? Change order the job for his more space equals more costs in panel design and material.

 

[VAN]

all of my work is C1, D2 so nothing special about this job. we are an industrial process OEM.

Sorry ignore me, was drinking last night, but I've known of sites blowing up and others with ARC flash issues.

I don't have any evidence of the panel builder being the legal responsibility but for "safety" I say ignore the customer on the side of safety.

edit - 2012 Canada had a few sites blow up.

 

[ndzied1]

We have some customers that specify no AC in the control panel. We put the DC power supply in the high voltage panel and run the 24 supply to the control panel. These are usually for large plants. They know what they want and they know what it costs. As Milldrone mentioned, I have to believe it is because they are actually following NFPA 70E for PPE.

 

[James Mcquade]

Van,

i've been in the business of panel building and working for oem's for 30+ years and have seen all sorts of customer requirements. Separating the 120 from 24 volts used to be common and is still a requirement from some companies. they have their reasons and to them, it is an additional safety measure since this is a class 1 div 2 environment. having worked in a munitions plant for 8 years, i definitely understand. this requirement violates no electrical code that i know of.
as far as the legal responsibility of the controls design, the responsibility belongs to the design company. we built a system that was modified by plant maintenance and someone got hurt. the company tried to take us to court. needless to say that the company was not happy when they found out who was responsible. we are in a lawsuit happy country and everything must be documented, customer specs, modification requests, proposals, designs, programs, change orders, emails, faxes, email follow up on all phone calls, everything!
YES, this is long winded, but i hope it keeps someone else out of the legal troubles i have been in and seen. We had a change order from the customer, signed by their engineer, that scrapped over $400 million in materials and parts, plus a product recall. that one document saved my company and me - i made the program change.
james