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 Post subject: 1200 amp switch, 240 volts service
PostPosted: Tue Apr 29, 2014 8:53 am 
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Hi- I am new at this forum, and could use some advice before I have an arc flash analysis done. I have an older building, with service updated in the 1970's. Everything is served by 240 V 3phase , through a Westinghouse FDPS 368M disconnect rated at 1200 amps. The former occupant was a bakery, which needed far more power than we are using. Is there anything that should be done with fusing, or anything else, that would limit my arc flash hazard?
I have not had an analysis done yet.
Also, I am currently working on a plan for organization and labelling all of the switchgear, panels, and outlets in the building. Is there an accepted or recommended naming/numbering sequence for this purpose? Several electricians I have asked do not know.


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PostPosted: Tue Apr 29, 2014 10:19 am 
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1. 240 VAC is kind of a funny animal. I can virtually guarantee that when you run the arc flash hazard analysis, that breaker in particular is going to be rated extremely high. However somewhere below around 250-300 V in the real world, the existing models tend to fall apart because they only predict incident energy with nice, stable arcs. There is only a very small number of data points in the data set used to calculate the IEEE 1584 empirical model for instance. So at best you are going to get "conservative" (way too high compared to reality) results from an arc flash study. That being said, first to the study then look at what to do about it. Chances are that if you address issues with the one big breaker, everything else will be reasonable. Second, unlikely that breaker is even in calibration anymore. I'd recommend doing the study with an intention to replace it. I'll give you 80% odds that if you test it, you'll find it is way out of specification, IF it works. And the arc flash study is worthless if the breaker won't trip in the first place.

2. There is no general naming/numbering scheme other than what makes sense to you. Some folks do it by some sort of scheme that involves the single lines. Some do it with some kind of "local" naming referring to different areas that makes sense. Some just take whatever the software gives for a default number. As long as everyone understands how it works and it's easy to use, it is acceptable.


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PostPosted: Tue Apr 29, 2014 11:23 am 
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"Chances are that if you address issues with the one big breaker, everything else will be reasonable. Second, unlikely that breaker is even in calibration anymore. I'd recommend doing the study with an intention to replace it. I'll give you 80% odds that if you test it, you'll find it is way out of specification, IF it works. And the arc flash study is worthless if the breaker won't trip in the first place."

In order for me to understand the terminology correctly, this is a fusible disconnect, with class R or J fuses. Would you refer to this as a circuit breaker?
Also, thanks for the labelling answer.


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PostPosted: Tue Apr 29, 2014 11:45 am 
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Scott,
Paul provided some good answers and advice. Yes, he did refer to your fusible disconnect as a breaker but they both accomplish the same function which is to "break" the circuit.
I agree that manual operation of the switch could be problematic if it has not been maintained. There could be lubrication and contact pressure issues. The fuses will operate but will the switch be able to be opened to replace fuses and closed afterwards?

The first step would be to have a study done. If you are using less power than the previous building occupant, smaller fuses could be utilized. Smaller fuses may reduce the downstream arc flash hazard but a study would be needed to determine. Regardless, the main switch will be a high arc flash hazard as the protecting device would be the utility fuse on the primary side of the transformer.

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PostPosted: Tue Apr 29, 2014 12:00 pm 
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I was just pointing out that there would be no way to "calibrate" my fused unit. It is located indoors, in a dry, heated area so I imagine it could be opened without trouble.
Thank you both.


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PostPosted: Tue Apr 29, 2014 12:24 pm 
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A word of caution - don't assume it could be opened without trouble. There could be things such as the mechanism will not move since it has not been lubricate, the operate mechanism/linkage could be faulty, blade welded to mating contacts due to overheating, etc. and you THINK you have opened the switch but only moved the handle not the operate mechanism.

I know of one case where a fused disconnect similar to yours was opened to replace a fuse. The individual did not perform a voltage check, did not have PPE on and did not use a fuse puller. When he tried to remove the fuse with channel locks, he created a short with a resulting arc flash. The operate handle moved to the open position but the contacts never opened because the linkage between the handle and contacts was broken.

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PostPosted: Tue Apr 29, 2014 2:04 pm 
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Good point. I think this will be addressed more completely in the near future. I have replaced ALL of the bus plugs in a separate Square D panel because the operating mechanisms were broken or unreliable. Those were Saflex QMB 310 Series 1 , 100 amp switches. They were replaced with Series 4 parts, which hopefully are better made.


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PostPosted: Wed Apr 30, 2014 6:03 am 
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I missed the fact that its a disconnect. Disconnects tend to be vastly more reliable than breakers partly because the majority of failures with breakers are either in the trip unit itself or in the trip mechanism itself. Since the disconnect mechanism is a lot simpler it tends to have fewer problems. Reliability is usually 2 orders of magnitude better as a result.

As to the fuses, they do fail occasionally. I've seen them fail by tripping more quickly than they are supposed to when they age (20+ years old). It is possible for them to fail to trip but this is a lot less likely.

Replacing fuses with newer modern fuses, even if the current is exactly the same, can definitely result in lower arc flash ratings. It can sometimes result in actually increasing arc flash ratings but this is more rare.

There are even fuses which are intentionally designed with more steep curves than the standard calls for which improve this even further as long as they are replaced with identical fuses. There is not much room for improvement in this regard with class J fuses but there is a huge amount of room for improvement in the class R (usually RK) series.

Fuses are limited in their ability to coordinate and address single phase loss issues. But if you can design around their limitations, fuses definitely have a speed advantage and installation costs are usually lower than breakers. As long as you maintain the disconnect, I'd feel very comfortable with an all-fuse distribution system in terms of electrical hazards.


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PostPosted: Fri May 02, 2014 8:49 am 
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I just received word from my electrical supply distributor that an arc flash analysis from Schneider would cost upwards of $10,000.00. This seems outrageous to me.
Is this out of line? Would an independent contractor be less expensive? I am located in the midwest, 90 miles from Chicago.


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PostPosted: Fri May 02, 2014 12:46 pm 
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It depends on many factors. Are they going to do data collection or will you provide all the data needed from in house sources? Does the study include short circuit, equipment duty, coordination with time current curves in addition to arc flash hazard analysis?

Typically if you go with a small independent company, their overheads are not as much as a larger company such as Schneider, Eaton, etc.

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PostPosted: Fri May 02, 2014 1:26 pm 
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Scott Peterson wrote:
I just received word from my electrical supply distributor that an arc flash analysis from Schneider would cost upwards of $10,000.00. This seems outrageous to me.
Is this out of line? Would an independent contractor be less expensive? I am located in the midwest, 90 miles from Chicago.


It all depends. There are too many variable to give an 'always' answer.

Typically 50-60% of the cost of the study is the collection of the data required to model the system. Buildings with many panels spread across multiple floors without an accurate one-line can take a surprisingly long time to collect data. We have many customers that take this task on themselves, probably fewer than 30% feel they would do so again. If you guess at the input data, you might as well guess at the output results.

The next largest cost is if you are asking for engineering time to design and evaluate alternatives for mitigating any findings. This is one area where low cost providers cut corners. My group is currently working on 4 mitigation projects where we were not the original study supplier.


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PostPosted: Fri May 02, 2014 1:49 pm 
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JBD wrote:
This is one area where low cost providers cut corners.

You are being too polite in your description. I know of a couple of companies where the term "con artist" might be more appropriate. It is great to hear you are working on mitigation projects instead of a conclusion I frequently hear: "oh well, the incident energy is really large so sorry, you will have to wear the bee keeper suit - in the summer"
Keep up the good work!


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PostPosted: Fri May 02, 2014 2:21 pm 
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I assume the "one line" is the complete path from entrance to outlet. Can anyone direct me to a diagram or document that shows an example of this ?
I am in the process of doing something like this now as part of labeling. Fortunately I have been here for a long time so most of this is fairly well understood. It is still beyond me that there does not seem to be a standardized way of doing this labeling.
I am far less concerned with the OSHA regulation than with keeping my employees and myself safe. So understanding the PPE required for a given area is part my goal. Telling me it will cost 5 or $10,000.00 just goes against my better judgement. So far.


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PostPosted: Fri May 02, 2014 4:41 pm 
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Square D's accuracy for our arc flash study was embarassingly bad. It did not help that we went through 3 or 4 different engineers at our facility because they couldn't seem to keep anyone on their staff for very long and each one essentially started over from the beginning. Their idea of mitigation was even worse. Basically they ran just two scenarios. Scenario #1 was "as-is". Scenario #2 assumed that ALL breakers, everywhere were turned down to lowest settings on instantaneous, whether this actually made sense or not. That was even more unrealistic and did not account for interactions among breakers as a result. I would not use them again. Granted this might just be an issue with the Raleigh office but when the cost of the arc flash study was over 10 times what you were quoted, I would have expected it to be handled much better.

The best option if you can stomach it is if you do the data collection yourself and pay only for the engineering time or else look for a low cost "data collector" service because that's where all the labor costs are at. Remember...basically every breaker and fuse make, model, and settings, every cable, and every transformer has to be documented, at least down to a certain level. This is very time consuming. I update the model myself and it takes about a day to update even the area covered by one project with new switchgear or MCC's. Granted part of the time consuming part is that since I'm starting out fresh, I automatically run all kinds of extra scenarios and tweak settings to find the most optimal configuration. If I was not running arc flash scenarios, I would do at least 50% of the same amount of work anyways.


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PostPosted: Mon May 05, 2014 5:48 am 
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Scott Peterson wrote:
I assume the "one line" is the complete path from entrance to outlet. Can anyone direct me to a diagram or document that shows an example of this ?

Try the SKM site under support to start.
http://www.skm.com/faq_ptw5.html


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PostPosted: Mon May 05, 2014 8:31 am 
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Scott Peterson wrote:
It is located indoors, in a dry, heated area so I imagine it could be opened without trouble.
Thank you both.


As others have said, that is a BAD assumption. At that size I would assume that it is a "bolted Pressure Switch" of some form or other.
And as said by others they have a bad habit of sticking part way open, or part way closed.
In a bakery, I would EXPECT you to have some issues. yeasrs of decades of built up flour dust on critical surfaces, slowly oxidizing and carmelizing.......

When they are in good shape, they can be good at what they do, but IMO they cost less than a breaker for a reason.
============
THe "oneline" is your electrical drawing of the system. Called a "oneline" because One line is used to represent the three phases and neutral conductors. It is at the heart of everything elese you do with the electrical system.

============
As Paul Said, the data collection is very important, and is the most expensive single part of a study. Finding some one who can do it well is hard.

==============
The best (overall) naming scheme I have run across (used by a quasi governmental org) starts at the top level of the power system for that building (say Bldg 57) and assigns it a Single letter or two letter ID, say "A". So that Panel is "B57A". Each breaker fuse or whatever, in "A" is given a number (following a ".") so the third (non main) breaker is "B57A.3". The load that breaker feeds is called "B57A3A", and if another panel is sub fed out of B57A3A, from poles 5-7-9 of the panelboard, then that load is B57A3A5A.

In the Case where multiple loads are fed from a single breaker, then B or C would be used rather than "A" for the 2nd , 3rd etc panels.
In the above if B57A3A was bus tapped to another panel, it would be B57A3B.

In this way you can always tell where a panel is fed from by its name.
And it is possible to give EVERY electrical device a unique name, down to light switches and receptacles.

The down side is VERY non memorable names, that can be quite long in a complex power system.
Also if you change the name of ANY thing upstream, EVERYTHING downstream has to get changed.


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PostPosted: Mon May 05, 2014 8:54 am 
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You have to ask yourself how important it is to know where something is fed from. Is it easier to even just put a sign on the panel that reads "fed from XXX". This approach flattens the label hierarchy down considerably and allows you to get more creative with panel naming, using more memorable names since you then have a flat hierarchy. I've also seen it done where the hierarchies always start over any time that a new ground plane is established. This usually happens whenever we go through a transformer so for instance the inter-building/plant distribution network would be one hierarchy but the moment that it steps down to utilization voltages, the hierarchy starts over.

Both of these solve the problem of very long names and/or the issue that changing feeds at the top causes a huge cascade of label changes.


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PostPosted: Mon May 12, 2014 7:36 am 
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I was a data collector for 7 years for two different companies. If you know your system and all panels are labeled, the data collecting should be a simply process. Most customers do not have good one-lines, and that is why it is so labor intense. Having your panels labeled is a good start. The second important part is having a good maint. tech or someone from you organization, that can work with the data collector. This person must know your plant and have a good idea how panels and machines are fed. Once you have a good set of one-lines, and you keep them updated, your future studies will cost much less.


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PostPosted: Mon May 12, 2014 9:05 am 
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Thank you all for your valuable advice. I started out with the task of labeling circuit breakers, but mapping the whole system as I am now doing has obvious benefits. It is all preliminary groundwork with a long term benefit .


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PostPosted: Wed May 14, 2014 5:17 am 
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Scott
I work for a multi national company and am based in the UK.

We work closely with the University of Strathclyde and have just released a recent white paper which should be extremely helpful.
log on to gses.com and set up an enquiry and I will contact you.


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