Code changes affect the plant floor
The National Electrical Code typically views an industrial control panel as a piece of equipment with proper installation being the major concern. Titled the “Standard for Safety for Industrial Control Panels,” UL 508A covers industrial control panels intended for general industrial use, operating from a voltage of 600 V AC or less.
The National Electrical Code typically views an industrial control panel as a piece of equipment with proper installation being the major concern.
Titled the “Standard for Safety for Industrial Control Panels,” UL 508A covers industrial control panels intended for general industrial use, operating from a voltage of 600 Vac or less. This equipment is intended for installation in ordinary locations, in accordance with the NEC.
Short circuit current rating
On April 25, 2001, UL 508A was issued; on April 25, 2006, this requirement became effective. Part of this standard requires short circuit current rating (SCCR) to be marked on industrial control panels. Although UL 508A affects OEMs, machine builders and panel builders directly, it also affects your plant indirectly through the NEC, which does affect your plant directly. When applied to your plant, these rules and codes determine how you specify equipment, how equipment is inspected, the relocation of equipment and equipment maintenance.
NFPA 79 is the standard to which machine builders, OEMs and panel builders must build industrial machinery. However, NFPA 70, otherwise known as the NEC, is the standard to which equipment must be installed, which affects you directly. It is important to understand the NEC, as well as the standards and regulations that support it. This understanding becomes critical when adding equipment to your plant.
“If a short circuit occurs, you want the overcurrent protective device to do its job without worrying whether a contactor or motor starter will act as the fuse,” said Todd Lottmann, senior technical marketing engineer at Cooper Bussmann. “SCCR is not an interrupt rating; it is a withstand rating. It identifies the first part likely to blow up if a short circuit occurs in certain locations within the circuit. It identifies the weakest link in a single power circuit within an industrial control panel. A panel may contain several branch circuits that are fed from one or more feeder circuits. Circuit configurations affect how SCCR for the panel is determined.”
Most companies contract with suppliers, such as OEMs, machine builders or panel shops, to fabricate control panels to accompany plant-installed machines. Other plants prefer to build them inhouse. Regardless, specifications are required to include what is in the panel, how it must function and how it is to comply with existing regulations.
It is important to understand NEC requirements in effect in your jurisdiction when specifying equipment. It is also important to understand the requirements of UL 508A — especially as it applies to short circuit current ratings. When specifying equipment, one of the first things that plant engineers and managers must determine is available fault current. This should be listed somewhere on the utility bill. But this is just the beginning.
If you choose to build your own control panels, defining the specification can be difficult, as can determining SCCR. “UL 508A has many requirements beyond SCCR,” Lottmann said. “These requirements include type of enclosure, conductor ampacity, circuit protection and much more. Building your control panels inhouse is becoming much more difficult that it used to be.”
“An assembly rating is the interrupting rating of everything inside the panel,” said Lottmann. “When determining SCCR you must determine your interrupting rating, your component rating and whether you can 'fix’ your component rating. The ability for a protective device to limit current is the key to enabling industrial control panels to have a higher SCCR.”
The easy way out is to procure the panel from a listed supplier with third-party certification to all applicable standards — including UL 508A. “I think the best advice I could give is to require that the piece of equipment be listed — third-party certified” said Jim Pauley, vice-president of industry and government relations at Square D. “And when you do that, all the nuances about UL 508A get handled as part of the listing. The NEC does not require the control panel to be listed. But it does require that it has a short circuit current rating.”
“What I think will happen, which could take a couple of years, is that end users will say, 'Just give me a listed control panel. I’ve got 22 kA available fault current; I need a listed control panel that does these things, but carries an SCCR of 22 kA.’ I think that is ultimately how they will solve their problem,” Pauley said.
When a new piece of equipment is installed, it must be inspected before power can be applied. The permit process triggers the inspection. After the inspector is satisfied that the equipment is electrically safe, he or she signs off on the permit and you are allowed to apply power.
“There are jurisdictions that require an electrical permit when any electrical work other than maintenance and repair is done in the facility,” Pauley said. “Then that permit triggers the inspection time-line that will occur, and the contractor would call for an inspection (when the work is being done by outside contractors) at certain stages depending the particular work being done. Contractors are very familiar with the inspection system. Getting the inspector in and pulling a permit is pretty routine.”
When equipment installation is done using a facility’s electrical workers, there typically is a gray area between whether it’s considered maintenance and repair, or if it’s considered installation. Pauley said, “If I move a machine over 10 feet, is that maintenance work or is that new installation work? Honestly, the local jurisdictions have to deal with it. And I think in a lot of cases where plants do that kind of work, it is treated as maintenance work and probably not inspected.
“NFPA Article 409 (2005 version) does not outline at all, as a matter of fact the NEC in total, does not outline when an inspection is required, or how you do the inspection,” Pauley added. “The NEC only outlines the applicable rules for an electrical installation. So the local jurisdiction is really responsible for what’s required to be inspected, when is it required to be inspected and who is going to do the inspection.
“There are examples where cities have agreed with large industrials to do an annual inspection. The plants keep track of the (electrical) work that they’ve done throughout the year. When an inspector comes in, he or she may pick some of the particular work that was done and do an inspection on them after the fact.
“Most jurisdictions for electrical inspectors will say that they can only barge into a facility if there is a known hazard that they are going in to actually resolve. If they get a report that there are all these loose wires hanging down in here and people have been shocked multiple times, the inspector probably has cause to be able to inspect unannounced. But, I don’t know of any case where that’s been done. The inspector is willing to work with you on all these points.
“Once a state adopts the code, typically, no one is exempt except the electrical utility. But, whether it is inspected or not, does not excuse you from the legal requirements to comply with the code.”
However, not every state has adopted the 2005 NEC. As of press time, 26 states have adopted the 2005 Code, as have a number of local jurisdictions where the states don’t adopt.
“I think companies and inspectors are looking for the same thing — they want it to be safe, they want it to be compliant and they want to make sure they’ve done it the right way,” Pauley said.
Moving equipment from one location to another depends on the distance it is moved and the jurisdiction. Requirements may differ according to whether equipment is moved within a building, from one building to another or across state lines.
“If a production line goes from “L” shaped to “U” shaped, or if a piece of equipment is turned or its position is changed, then it may need new conduit run to it,” Pauley said. “But the machine probably has not substantially changed in that case. Most jurisdictions put that under the maintenance category.”
But if equipment is moved from one state to another, even though it is within the same company, most inspectors will view that as new equipment coming in. “You are adding to the facility just as if you added onto your home by putting in new wiring, and therefore a permit would be required,” Pauley said.
With equipment crossing state lines or moving several feet across the plant floor as extremes, scenarios that fall within this continuum will be left to the discretion of the inspectors. “Some of these decisions will still be made locally,” Pauley said. “We have the NEC for the rules, but how the inspection is done has not been standardized.”
If you perform maintenance on an industrial control panel, you may affect its SCCR, which would cause it to no longer comply with UL 508A.
“We encourage facilities to make sure they keep up with the modifications they do,” said Pauley, “because that could change the SCCR. You may have a control panel that has been in your plant for five years with a 5 kA SCCR and 22 kA available. You may say, 'it has been there for five years, and we haven’t had any problems.’ It’s only because you’ve been fortunate enough not to have a short circuit. Electricity is a great thing. I can underrate and miss-size everything. And as long as I never load the system, no one ever knows. But when it’s finally called upon to do its job, then things cut loose, and then you really know it.”
Not every maintenance task performed on industrial control panels warrants another inspection. If a component is changed in any power distribution path, SCCR may be affected. Control circuits are exempt. If you replace a component with the same part number from the same manufacturer, the SCCR is not affected.
“People are viewing SCCR like short circuit is something new,” Pauley said. “It’s always been there, but now that there is more attention called to it, suddenly by pulling out a motor starter from XYZ and putting in the same size starter from ABC, you may have changed the SCCR of that panel from 22 kA to 5 kA. You have to know what you’re replacing, what you’re replacing it with and if it maintains the rating you would have had. From a UL listing aspect, if you replace it with something that’s marked on the diagram, then the listing is still ok. But if you replace it with something that’s not on there, then UL can’t tell you what that does to the listing because they haven’t evaluated it.”
In cases where you need to replace an obsolete component, it may be difficult to determine what your selected replacement does to the rating. Some third-party inspection companies offer field evaluation services that will examine your modifications, evaluate their impact and determine suitability. Sometimes it’s necessary to contact the manufacturer of the intended replacement component to ask for further test data or information that could be useful in determining the SCCR.
Some manufacturers are working with UL to compile comprehensive databases that list tested combinations of components. This option can save time and money because only a field inspection would be required. This inspection is typically to witness the label being changed to recognize the rating of the new component. Although there is cost associated with the inspection, it is still less expensive than a field evaluation.
Tested device combinations have a UL record number, which is used as a reference when determining SCCR, according to Lottmann. However, the information is good for that combination only. Once the component or combination is installed into the control panel as part of an upgrade, for example, it does not take upstream circuits into consideration.
“There may be two other existing branch circuits that still have only a 10 kA rating, which means that the panel is only good for 10 kA,” Pauley said. “We’ve given them a 42 kA combination (for example). The objective of doing the database is that anyone — an inspector, a facilities engineer — would be able to access the database and determine the rating when using this component with that circuit breaker. But the UL number is primarily going to mean something only to the person building the control panel. I can give you a UL number for a circuit breaker. But if I install that circuit breaker in a panel with other components, all I have is a listed circuit breaker. It tells me nothing about whether I have a listed assembly that it went into.”
Whereas the UL number is of more value to the panel builder, the databases will be of value for inspectors and end users. The database plays an important role when doing a field evaluation because the nationally recognized testing laboratory doing the evaluation can use the listed combination in relation to all the applicable circuits in the control panel, which expedites the field evaluation.
As inspectors concentrate on industrial control panel SCCR compliance, plant engineers and managers should become more familiar with how UL 508A and the 2005 NEC work together, and how they affect equipment specification, procurement, installation and maintenance at your facilities.
The Bottom Line...
Part of UL 508A requires short circuit current rating to be marked on industrial control panels.
When specifying equipment, consider procuring the control panel from a listed supplier with third-party certification to all applicable standards — including UL 508A.
If you perform maintenance on an industrial control panel, you may affect its SCCR, which would cause it to no longer comply with UL 508A.
For more info
Refer to UL 508A, Supplement SB to determine the requirements for calculating and labeling SCCR on each control panel.
Plant Engineering magazine will present a free Webcast titled ”Control Panel Compliance” on Wednesday, June 21, 2006 at 10 a.m. CDT. Learn from our panel of experts what your responsibilities are when upgrading and specifying equipment for your plant, how to comply with current regulations and how to minimize the potential for equipment damage or injury to personnel. Visit
Control Engineering magazine will present a free Webcast titled “Understanding the Impact of UL 508A” on Wednesday, May 17, 2006 at 11:00 a.m. EDT. In this Webcast, the panel of experts will walk through the Code changes, the new UL Standards, what it means to panel builders and examine alternative solutions that enable a fast adherence to meet Code requirements for an overall SCCR panel rating. Visit
- Events & Awards
- Magazine Archives
- Digital Reports
- Global SI Database
- Oil & Gas Engineering
- Survey Prize Winners