Voltage drop

[ohmhead]

I have a panel that the engineer states the demand load is 19 amps its a 42 crt 225 amp 3 phase 480 volt panel.
There is only two breakers used and they are rated at 30 amps each and 3 phase. All the other breakers in panel are listed as spares this is in the panel schedules and its not a mistake .
My question the rule for voltage drop needs the load in amps to calculate the drop. So does the NEC just go by the actual load at the time of calculation?
I feel a 225 amp panel with 42 crts can be loaded and trip in the future what's your thoughts . As far as voltage drop when calculated at 19 amps demand its ok but if its loaded high it will drop the voltage down below the 3% or 5% required. I also feel its a poor design as the breaker feeding this panel is a 225amp.

So how does the rule on voltage drop work is it the load in amps that rule at that moment in time ?

 

[iwire]

The NEC does not require voltage drop calculations for that application.

If you have an energy code to follow I would be willing to bet the calculations are done based on the load at the time and not what can happen in the future.

If someone does add load to the panel it is their responsibility to remain code compliant.

 

[ohmhead]

The NEC does not require voltage drop calculations for that application.

If you have an energy code to follow I would be willing to bet the calculations are done based on the load at the time and not what can happen in the future.

If someone does add load to the panel it is their responsibility to remain code compliant.

Thanks we didn't write a RFI to engineer because we were thinking what you stated above but common sense is what we were using for the future .
So what ever the load is no matter how large the panel is rules on Voltage dropped. So a 2000 amp panel could pass inspection with 19 amps load if it was 1000 feet from main breaker. As long as the load never increase. And the owner is responsible for adding a load to a panel.

What is a energy code ?

 

[Ingenieur]

Is the feeder pulled? What size and dist from source to panel
I would run it at 80%
if it passes, good to go
if not just back calculate from the desired v drop to get the amps
if > 19 sounds like you're good to go

 

[kwired]

Thanks we didn't write a RFI to engineer because we were thinking what you stated above but common sense is what we were using for the future .
So what ever the load is no matter how large the panel is rules on Voltage dropped. So a 2000 amp panel could pass inspection with 19 amps load if it was 1000 feet from main breaker. As long as the load never increase. And the owner is responsible for adding a load to a panel.

What is a energy code ?

Energy efficiency codes is what he is talking about. Voltage drop occurs because of resistance in the conductors, and this is an inefficiency as it produces losses, less loss because of lower resistance conductors = more energy efficient.

 

[highlegdelta]

I'd say most 225a panels I see have 100-125a loads. I think 80% loaded panel is a bit high for a panel essentially put in for future use. I would do my voltage drop calcs at 125a and see where it's at. Although I doubt your situation breaks any code, if they didn't account for future loads in a spare panel for voltage drop then it's just a poor design.

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[Smart $]

I'd say most 225a panels I see have 100-125a loads. I think 80% loaded panel is a bit high for a panel essentially put in for future use. I would do my voltage drop calcs at 125a and see where it's at. Although I doubt your situation breaks any code, if they didn't account for future loads in a spare panel for voltage drop then it's just a poor design.

If the engineer didn't account for voltage drop of future added load, I'd have to wonder what the cost of that fully loaded panel was compared to a smaller panel, even a bare bones panel with two separately-purchased 30A 3P breakers...

 

[Fitzdrew516]

Agree with all of the above. However, when I design to a panel I usually design voltage drop using the capacity of the panel because I know that later on some maintenance guy is going to add a big motor load to it. It is correct that you only have to design per the current load, but I'm of the mind that it's easier to do a little work now than a lot of work later. That's what I usually do at least. Most of the time it might only up-size the conductors/conduit slightly, however, if it's a 500 foot run or something like that I may back it down a bit. Every situation is different.

 

[iwire]

However, when I design to a panel I usually design voltage drop using the capacity of the panel because I know that later on some maintenance guy is going to add a big motor load to it.

Isn't that a decision that should be made by those paying for the work?

 

[Strathead]

Thanks we didn't write a RFI to engineer because we were thinking what you stated above but common sense is what we were using for the future .
So what ever the load is no matter how large the panel is rules on Voltage dropped. So a 2000 amp panel could pass inspection with 19 amps load if it was 1000 feet from main breaker. As long as the load never increase. And the owner is responsible for adding a load to a panel.

What is a energy code ?

In Florida, they only modify the NEC in a couple of ways. One of those is voltage drop. Florida building Code requires 2% max on feeders and 3% max on branch circuits. As stated earlier, this is not a requirement of the National code. To answer your question, yes, if the panel passes voltage drop at the time, it is legal. It is unlikely someone would design a panel as you said any more than someone would wire a commercial space and not provide a single receptacle. Even though that would also be legal in many circumstances. On top of all that, your post doesn't have enough information to even let us understand how bad this issue is you are questioning. What is the distance and the feeder size?

 

[Fitzdrew516]

Isn't that a decision that should be made by those paying for the work?

Logically speaking, yes. But most of the time for the jobs I work on the owners don't know what they're adding 3 months later and they don't understand potential implications of blowing motors. So it's easier for me to size it this way instead of having them yell at me 6 months later for "not designing it right" after they've overloaded the once properly designed system.

 

[kwired]

Logically speaking, yes. But most of the time for the jobs I work on the owners don't know what they're adding 3 months later and they don't understand potential implications of blowing motors. So it's easier for me to size it this way instead of having them yell at me 6 months later for "not designing it right" after they've overloaded the once properly designed system.

If they are a good loyal customer they trust you to do what is right, and trust you to ask them for certain information at the right moments.

If they are a one time customer and this is a one time bid, the guy that designs it for what is there now often wins the bid.

You may get the chance to upgrade it next time when they add some load though.

 

[iwire]

Logically speaking, yes. But most of the time for the jobs I work on the owners don't know what they're adding 3 months later

If the owners don't know I certainly don't know.

I have pretty much given up wiring for the future, no one says thanks.


I once ran new circuits to a Square D 225 amp MLO panel. I really wish I had opened it before I ran the new circuits to it. When I opened it I found it was supplied with 10 AWG from about a 5 kva transformer.

Live and learn, never assume the panel has the capacity it seems to have at first glance. We re-routed the new circuits to another panel.

 

[Fitzdrew516]

If they are a good loyal customer they trust you to do what is right, and trust you to ask them for certain information at the right moments.

If they are a one time customer and this is a one time bid, the guy that designs it for what is there now often wins the bid.

You may get the chance to upgrade it next time when they add some load though.

Most of our clients are returning clients as my firm is in a particular niche market (Food Processing Plants). So it makes sense to keep the customer happy with your design even when he/she adds a bunch of stuff to it you weren't expecting. Although a design of actual load is all that is required, when something happens down the road because of unexpected additions or something of that nature, even though it was design properly at the time the owner(s) don't always see it that way. All they know is 1) it doesn't work, 2) I designed it. If I design with this contingency it's more likely we get the return business.

 

[Fitzdrew516]

When I opened it I found it was supplied with 10 AWG from about a 5 kva transformer.

:lol::slaphead:

 

[kwired]

Most of our clients are returning clients as my firm is in a particular niche market (Food Processing Plants). So it makes sense to keep the customer happy with your design even when he/she adds a bunch of stuff to it you weren't expecting. Although a design of actual load is all that is required, when something happens down the road because of unexpected additions or something of that nature, even though it was design properly at the time the owner(s) don't always see it that way. All they know is 1) it doesn't work, 2) I designed it. If I design with this contingency it's more likely we get the return business.

That is where your familiarity with the client or type of client and their typical needs comes into play. You better know what is likely to supplement something already there then someone that typically does work for steel mills may be aware of, but you might not know what to be prepared for if it were a steel mill.

 

[iwire]

:lol::slaphead:

If only someone took a picture of my face when I saw it. :rant:

I had gone out and priced the work about a week before, the panel was a 225 amp full of empty spaces. I was looking to add a 2 pole 30 and a single pole 20 for a new split system and service outlet for it. I assumed the panel would have the capacity.

 

[kwired]

If only someone took a picture of my face when I saw it. :rant:

I had gone out and priced the work about a week before, the panel was a 225 amp full of empty spaces. I was looking to add a 2 pole 30 and a single pole 20 for a new split system and service outlet for it. I assumed the panel would have the capacity.

Did you miss the fact there wasn't any raceways larger then 3/4 entering it? Or did they run 10 AWG supply in a 2-1/2 inch pipe?

 

[iwire]

Did you miss the fact there wasn't any raceways larger then 3/4 entering it? Or did they run 10 AWG supply in a 2-1/2 inch pipe?

It was flush mounted in an office wall.

I do recall they had stripped the 10s long and folded them up to make the large lugs hold onto them.

 

[highlegdelta]

Did you miss the fact there wasn't any raceways larger then 3/4 entering it? Or did they run 10 AWG supply in a 2-1/2 inch pipe?

I had a similar situation, although I happened to notice before I did any work. It had a 2 1/2" conduit but #8s pulled in a separate pipe back feeding the panel on a 50a breaker. Turns out, when the last tenant had an electrician come disconnect their equipment, he also ripped out the feeders and the transformer that supplied the panel.

We made a few phone calls and a couple guys show up two hours later with the transformer they stole. Never got the feeders back though.

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