Survey??

[hawkeye23]

I will try this post again , lost my work here. After a arc flash survey a company recommends changing the trips on the switchgear to lower the hazard to a level 2 from a 4. Can operating these cb's remotely be another way to do that safetly ? Also they determined that the mcc's were at a level 4 at the line side of of each main cb but I did not see any mention of the load side buckets. Should they have their own rating or is the highest level used on the labels?

Don't know much about how this works , if anyone has any input on this type of work we would really like to here it.
Thanks for your input in advance.

 

[jim dungar]

It is too bad that you don not have enough of a relationship with your study provider to get these answers from them.

Rarely are there actual right-wrong answers when in comes to interpreting/implementing arc flash study results. This is mostly on purpose as the NFPA 70E committees realize that each company needs to create their own Electrical Safe Work Practices program which covers there particular company. This is in the same vein as most OSHA regulations, you are told what to do and what the outcome (i.e. safe workers) must be, but there is little details on how to get there.

Remote operation of breakers is a method to reduce the the exposure of your workers to a hazard, while it does nothing to reduce the hazard itself. It is definitely a viable mitigation strategy.

For your MCC, many study companies will not consider an integral main device as reducing the incident energy in an individual bucket. Their reasoning is that an event in a bucket will propagate through out the MCC vertical sections and effectively bypass the main device. Other companies do not have this belief. To my knowledge no manufacturer has tested their standard construction in a manner that will let them conclusively state what will happen for all possible MCC configurations.

 

[zog]

I will try this post again , lost my work here. After a arc flash survey a company recommends changing the trips on the switchgear to lower the hazard to a level 2 from a 4.

Installing a maintenence switch is another option in many cases, changing the trip settings can be effective in mitigation but can lead to coordination issues if not done properly.

Can operating these cb's remotely be another way to do that safetly ?

Yes, what type of breakers are they?

Also they determined that the mcc's were at a level 4 at the line side of of each main cb but I did not see any mention of the load side buckets. Should they have their own rating or is the highest level used on the labels?

They should have labels based on the main breaker, did they not include that in the study?

 

[hawkeye23]

[Breakers are wwesthinghoue ds in switchgear .
If they r set to lower ie to below level 2

Could the. cb they feed at the mcc be above level2
Thanks for the help.

 

[petersonra]

Installing a maintenence switch is another option in many cases, changing the trip settings can be effective in mitigation but can lead to coordination issues if not done properly.

Is there some requirement that a switch be used? why couldn't you just change the setting on the Cb when you wanted to work? make it part of the procedure.

 

[zog]

Is there some requirement that a switch be used? why couldn't you just change the setting on the Cb when you wanted to work? make it part of the procedure.

No requirement for a switch, just easier to manage. The switch can be locked so access is controlled by a manager and an indicating light comes on to verify you have the quick trip settings enabled or not.

Or you can use a procedure and hope they remember to return the settings to normal.

 

[zog]

[Breakers are wwesthinghoue ds in switchgear .
If they r set to lower ie to below level 2

Yes you should be able to change the settings, or install a maintenance switch. Pages 81-83 of this catalog shows some remote switching options for DS. http://www.cbsarcsafe.com/catalog/#?page=82

Could the. cb they feed at the mcc be above level2
Thanks for the help.

Yes, very possible, but I can't say for sure without seeing all the data. That should have been detailed in your study.

 

[hawkeye23]

After reading all the responses here i have one more question . If done correctly can the maintence switches be replaced by changing the setting on the trip unit ? Maintence switches are used when doing live work on that circuit ?
Company is looking to save money since there were alot of MS [ ARMS ] recommanded.
Thank you all very much.

 

[zog]

After reading all the responses here i have one more question . If done correctly can the maintence switches be replaced by changing the setting on the trip unit ? Maintence switches are used when doing live work on that circuit ?
Company is looking to save money since there were alot of MS [ ARMS ] recommanded.
Thank you all very much.

Maintenence switches are used to decrease the clearing time and therefore reduce the arc flash hazard downstream of the breaker, typically not used for live "work", that should be a rare thing to do, but more often to do things like rack a breaker out for LOTO or remove a MCC bucket.

IF you have an INST function on your trip unit you can lower that setting and get a similar result as using a maintenence switch but you need to be careful about changing settings and forgeting to put them back or you will lose coordination. You also would have a 2nd arc flash label that is in effect when the pre-determined lower setting is used.

There are many options out there and the most economical choice for adding a switch will depend on what you have now for breakers and trip units.

 

[iceworm]

.... IF you have an INST function on your trip unit you can lower that setting and get a similar result as using a maintenence switch ....

Tell me how this works cause I don't see this at all. Turning down the Instantaneous setting does not change the impedance, available fault current, or the trip time. I don't see how it can affect the arc flash energy.

Don't most maintenance switches lower the short time? I'm thinking the arc flash energy is porportional to integral[i^2(t)], so the short time portion of the curve is probably the place where the energy is highest and can be affected by lowering the setting.

ice

 

[zog]

Tell me how this works cause I don't see this at all. Turning down the Instantaneous setting does not change the impedance, available fault current, or the trip time. I don't see how it can affect the arc flash energy.

Well maintenance switches are most effective in cases where you do not have INST protection (Which is common on main breakers), so I chose my words poorly there. Having an INST setting greatly reduces trip times over ST and has a huge effect. The arcing current can be very low but typically will not self sustain below 38% (Ibf) on 480V systems and can be as much as 85% (Ibf).

When you already have an INST setting it may or may not be effective depending on where it is set, the key here is the trip unit will see the arcing current, which depending on several variables can be much lower than the available fault current and may not be high enough to trip the breaker on INST if the setting is high. Lets say you have a 1600A feeder breaker in a system with 30kA available fault current, and the INST is set at 10X. Arcing current could be anywhere from 11,400A to 25,500A, if your INST is 10X it won't trip the breaker until 16,000A, so maybe it works, maybe not. In this senario lowering the INST setting to 6X would have the same effect.

Obviusly there is a lot more detail involved in determining these settings and every breaker needs to be looked at carefully to determine what the best solution is.

Don't most maintenance switches lower the short time? I'm thinking the arc flash energy is porportional to integral[i^2(t)], so the short time portion of the curve is probably the place where the energy is highest and can be affected by lowering the setting.

Most systems actually install a trip setting that is similar to the INST trip and another setting similar to a GF curve. Here is URC's version http://www.utilityrelay.com/PDFs/Data Sheets/QUICK-TRIP Data Sheet.pdf

 

[iceworm]

... Most systems actually install a trip setting that is similar to the INST trip and another setting similar to a GF curve. Here is URC's version http://www.utilityrelay.com/PDFs/Data Sheets/QUICK-TRIP Data Sheet.pdf

I looked at the curves in your example. The effect of the maintenance switch is to shut off the short time delay - go to zero short time delay. As I think you agreed with (kind of hard to translate), the maintenance switch does not reduce the fault current - just the time.

ice

 

[zog]

I looked at the curves in your example. The effect of the maintenance switch is to shut off the short time delay - go to zero short time delay.

Well, zero delay is a INST trip.

As I think you agreed with (kind of hard to translate), the maintenance switch does not reduce the fault current - just the time.

ice

Correct

 

[hawkeye23]

Guys, I have to say thanks for all the help you all have given. I just read a preliminary report with some recommands that I am trying to interpet. I am not trying to make any changes just trying to understand it here below.

" PPE category rating reduced from 4 to 1 for MCC- CB1 line side " , and HRC reduced from "dangerous" to PPE category 1 for cb-2 on line side."
They want to change the digitrip units on our switchgear cb's that feeds the mcc cb's [ 2 ] with newer digitrip units with arcflash reduction maintenance switch system. They say if any work is to be done on either the mcc cb 1 or cb 2 that the corresponding upstream switchgear breaker must be put into maintenance mode.

Are the two category ratings lowered because of the new trips or the added arms ?
Does this mean any work in any bucket in mcc is ppe rated to CAT4 or "dangerous" without arms ?
Does the arms make a difference to the ratings ?
Thank you guys again.

 

[zog]

Guys, I have to say thanks for all the help you all have given. I just read a preliminary report with some recommands that I am trying to interpet. I am not trying to make any changes just trying to understand it here below.

" PPE category rating reduced from 4 to 1 for MCC- CB1 line side " , and HRC reduced from "dangerous" to PPE category 1 for cb-2 on line side."
They want to change the digitrip units on our switchgear cb's that feeds the mcc cb's [ 2 ] with newer digitrip units with arcflash reduction maintenance switch system. They say if any work is to be done on either the mcc cb 1 or cb 2 that the corresponding upstream switchgear breaker must be put into maintenance mode.

Are the two category ratings lowered because of the new trips or the added arms ?
Does this mean any work in any bucket in mcc is ppe rated to CAT4 or "dangerous" without arms ?
Does the arms make a difference to the ratings ?
Thank you guys again.

Weird, I just reviewed a study like this today, I mean just like it. The recomendation of ARMS sounds like the right solution from what info you have provided. But if you are switching trip units to digitrip and ARMS from something else there are much less expensive options with as good or better kits. The study I looked at today already had digitrip 810's so adding ARMS was best solution for the money.

What breaker types and trip units do you have now?

 

[hawkeye23]

From digitrip 500 trips to 520 mc with arms.
I guess I am confused I though arms were inuse when in the maintenance mode only.

 

[zog]

From digitrip 500 trips to 520 mc with arms.
I guess I am confused I though arms were inuse when in the maintenance mode only.

A 520MC is used on Magnum DS breakers, and the "C" in there is for communications. Unless you are istalling all of the communications cables and MODBUS computer you won't be able to use the communications feature and you are paying maybe a grand more each for the trip units to have that capability. Complete wrong application, I would get another opinion.

What type of breakers do you have now?

 

[hawkeye23]

Zog, thanks 4 the early response.

The cb's r ds & dsl 206 800amp fr. Main is a ds840. Do not no about comm. setup. We use digatrip 500 @ this time . Are the ARMS used only 4 maintenance mode.
Thanks for allthe help.

 

[zog]

Zog, thanks 4 the early response.

The cb's r ds & dsl 206 800amp fr. Main is a ds840. Do not no about comm. setup. We use digatrip 500 @ this time . Are the ARMS used only 4 maintenance mode.
Thanks for allthe help.

Yes, the ARMS is just a switch you install that puts the trip unit in arc reduction mode, which is (according to Eaton) faster than INST (Not sure how that is possible). You can't just add it to a digitrip 500, you would have to swap put trip units to a model that ends with a 10 (510, 610, etc) and add the ARMS. a 510 will be the cheapest option for you. Whoever proposed a 520MC is trying to pull one over on you.

 

[hawkeye23]

I must say I really learned a lot in this tread like most all treads on here and can not say enough about you guys that take the time from your work and help some of us. I personaly don,t have someone that has the electrical knowledge most of you guys have to go to and pick their brain for information.
So I just want to say to all of you thanks for the help.