Arc flash hazard for single phase load

How do you evaluate single phase load in your arc flash study? Do you put labels on single phase panels? Thanks!

Is it too easy to answer?

You would have to use the 3 phase calculations which would be over kill. What voltage is the load? How much short circuit current is available? My experience has been to model to the panels, mcc's switchboards etc. and stop there. Perhaps other's have gone down to the single phase load level but I'm not sure it is necessary unless it is a huge load with a big breaker and lots of short circuit current. Plus, I'm not sure how you would do it with only three phase formulas.

Single Phase

As far as I know there is no method for calculating a single phase load to date. I do this method, label as CAT#0 PPE 4ft AF boundary with the correct voltage gloves (Shock protection) when working in the restrictive area.
Personaly, there are no right or wrong methods just set up a program go with it.

Single Phase Load calculations

You can calculate with ArcPro Software but check to see if the transformer meets the requirements of exclusion under IEEE 1584. LV single phase often will and you can use the Tables for PPE and labeling. Many folks are labeling even single phase panels. Others are only labeling 3-Phase.

For unqualified workers it is wise to put some kind of label on all panels.

I'm at a fairly large University/Medical Center in the midwest. I am using a software program by the name of "Volts" from Dolphin Software. We are labeling everything from 3 phase transformers to single phase 30 load centers at our medical center. The logic is the guy with the least amount of electrical experince will be resetting the breaker, that's the guy I'm trying to protect.

ETAP 7.0 (the latest version) does single phase arc flash calculations. See http://etap.com/downloads/ETAP_70_Brochure.pdf . Single phase arc flash is shown on page 3 under new features. I haven't had a chance to try it yet though.

Single Phase Load calculations

Don't know what ETAP is doing. SKM has added a calc which extrapolates the ArcPro Values from the NESC standard. Sweet way to do it but I don't know if the values hold up outside of the NESC table list. If you want them to be accurate you should use ArcPro directly. I think all the original IEEE work was on 3 phase but they did very little testing. I think around $60K of the $500K was on testing. Most is administrative overhead.

pressure relief

Hello sir/madam,

I am currently studying ARC flash in the panel and I have read that many panel builders provides Pressure relief to discharge the pressure, created during arc.

I want to know,

1. Is there any standard to design pressure releif?
2. How to decide area of opening for pressure relief.

Thanks
sanjeet

Single Phase

There are three solutions to the problem of single phase arc flash (Assuming that you are fed from a 240 volt source, or a 208 volt source with a transformer 125 kva or larger)
1) use the tables for 240 volt equipment and below. Beware though of the notes and limitations of that table.
2) calculate three phase, and divide by the square root of 3 (for 240 or 208 volt) or by 3 (for 120 volt). This could also be used for 480 volt systems.
3) take the position that sustained arc fault on a single phase source is not a practical concern, and label it a Cat 0.
Bear in mind, only 1 and 2 give you some level of technical backing. 3 may be reasonable and safe, but you are out on a limb.

Arc Flash Pressure Relief on Panelboards

To my knowledge the standards for panelboards don't provide for pressure relief sufficient to vent an arc away from a worker. The test methods for panelboards only cover bolted fault which has much less pressure than an arc fault.

Only the arc resistant standards have venting for worker protection in arcing fault. Take care when interpreting equipment tests and claims. The standards are really just catching up in the US on arc flash and equipment but the IEEE standards are starting to catch up.

Arc Resistant means something for arcing fault. Normal fault tests don't have much meaning.

If there is no standard for pressurerelief so how to decide the size of opening beaciuse you cant predict the arc time and so pressure.

but In case of MV panle they use some standard (Not sure) to design pressure flap at top of panel.

I went through many articles also where ther are relating total energy generated inside the panel and pressure in the panel,but again they have not clarified for selecting exact area of opening.

So can you plaese tell me thet IEEE standard, in which they covered the process of selecting pressure flap area.

sanj.wish

There is some confusion here. There is no such thing currently as "arc resistant" equipment for anything other than medium voltage metal clad and metal enclosed gear. For that equipment, there is an IEEE standard. In the standard, they hang pieces of light cotton material in front of the gaps in the doors and panels at a defined distance from the panel. Then set off an arc equal to the maximum that the equipment is rated for. If none of the material is scorched beyond a certain specification, then it passes. There is no engineering calculation or design standard involved at all in doing this. Thus you can't use it for prediction of any kind. There is no mention of how the panel is designed to achieve this. It is purely a performance test.

The standards are ANSI/IEEE C37.20.7-2007 and. EEMAC G14-1 (1987).

Second, there is an issue with this statement:
2) calculate three phase, and divide by the square root of 3 (for 240 or 208 volt) or by 3 (for 120 volt). This could also be used for 480 volt systems.

It is not always possible to even get a self-sustaining arc below 240 volts. There are some qualifiers though to this that are not 100% understood. At this time the IEEE 1584 standard just states that if the feed is less than 125 kVA from a single source, then no arc flash calculation need be done, mostly because it is unlikely that an arc can be sustained.

In addition however, it is not altogether clear that arcing faults are always 3 phase arcing faults. In most of the test data for arc-in-a-box the simulation was effectively of metal enclosed gear and three phase faults appear to form quite readily as the plasma/gas expands out over the nearby contacts. However when phase barriers or metal-clad gear is involved, it is definitely not a decided fact that full 3 phase faults actually develop in practice. And since the test data used in IEEE 1584 among others does not quantify the difference, you cannot safely assume anything and simply divide by 3 or the square root of 3 to get a "single phase" result for those circumstances. In the case of open air faults in particular, especially at medium voltage levels for which ArcPro was designed for, there is strong doubt that three phase faults ever actually occur. With the non-arc-in-a-box test results, IEEE 1584 or ArcPro or any other calculation method is probably equally accurate at both single and three phase faults. So at this point I would recommend using the standards as-is with no multipliers for guessing what a single phase arc actually does.