Measuring current

[encoreman]

We frequently have to go to very small buildings (12' x 30') and measure the determine whether the electrical system needs to be upgraded. They are generally served by a transformer that is 25 kVA or smaller. The voltage is 120/240. It is usually a 200 amp service. In the past, we just removed the dead front, clipped on an ammeter and jotted down values. The most important value is the total current, although branch values would be helpful.

The way I read NFPA 70E, in order for our folks to remove the dead front and take readings we must equip them with Category 1 PPE.

Is there another way to measure current?

Jack

 

[iwire]

Call the power company and see if they have the demand data for these buildings.

 

[encoreman]

Great idea

Great idea

Call the power company and see if they have the demand data for these buildings.

I will definitely start requesting this information from the owner. However, many of these buildings are not individually metered.

 

[mivey]

Call the power company and see if they have the demand data for these buildings.

I would not expect demand meters on 200 amp services. I usually don't recommend them until the panel gets above 225 amps or they need a 25 kVA transformer or bigger, or use above about 3,000 kWh/month on average, or use above about 5,000 kWh in a single month.

There are always exceptions, of course.

 

[encoreman]

One solution

One solution

One idea proposed:
Most of these sites have their own or shared backup generator. We could open the disconnect at the meter (let the generator power the UPS panel), attach one of the new fluke meters with remote reading, reconnect the disconnect, wait for the generator to stop, read the meter and then put everything back...

I was hoping that some of you with more "practical" experience had a better solution.

It also prevents us from checking current in the UPS panel which is sometimes required.

 

[charlie b]

First of all, a 25KVA transformer with a 120/240V secondary will not supply a 200 amp service. So something is out of joint here.

But I believe that a panel that is rated 240 volts or lower and that is supplied by a transformer rated 125 KVA or less will automatically be a category 0 (safety glasses and leather gloves). That at least will be the results of any formal arc flash analysis, despite what is said in Table 130.7(C)(9)(a) of NFPA 70E.

 

[mivey]

First of all, a 25KVA transformer with a 120/240V secondary will not supply a 200 amp service.

Depends if they ever use 200 amps and for how long. Many a 200 amp panel is served by a 25 kVA or smaller transformer.

A 2500 sq ft total electric home around here would probably get a 25 kVA transformer and I'll bet it has at least a 200 amp panel.

 

[encoreman]

Need more information

Need more information

First of all, a 25KVA transformer with a 120/240V secondary will not supply a 200 amp service. So something is out of joint here.

But I believe that a panel that is rated 240 volts or lower and that is supplied by a transformer rated 125 KVA or less will automatically be a category 0 (safety glasses and leather gloves). That at least will be the results of any formal arc flash analysis, despite what is said in Table 130.7(C)(9)(a) of NFPA 70E.

Do I understand this right? If we do an arc flash study and the panels are Category 0, we can access the panel with Category 0 protection? Where is this documented? As you say, when I look at Table 130.7(C)(9) of NFPA 70E as soon as "Removal of bolted covers (to expose bare, energized electrical conductor and circuit parts)" the "Hazard/Risk Category" goes to "1".

It would make my life a lot easier if I am reading too much into this and I could use Category 0 PPE for taking current readings with the dead front off.

 

[zog]

Do I understand this right? If we do an arc flash study and the panels are Category 0, we can access the panel with Category 0 protection? Where is this documented? As you say, when I look at Table 130.7(C)(9) of NFPA 70E as soon as "Removal of bolted covers (to expose bare, energized electrical conductor and circuit parts)" the "Hazard/Risk Category" goes to "1".

It would make my life a lot easier if I am reading too much into this and I could use Category 0 PPE for taking current readings with the dead front off.

Did you do an arc flash study? If so you should have an Incident Energy on the label, and if so you only need the proper PPE for that level.

If no study was done and you use the HRC tables you have do follow those based on the task. You don't mix tables and a study. One is risk based, the other is hazard based.

 

[iwire]

I would not expect demand meters on 200 amp services.

That was why my suggestion was to see if they have it, not get it from them.