Main Distribution Panel with a Loud Hum

[electricalperson]

This to me is the way to go. Give yourself lots of headroom with the power. Why stress stuff out to the max? To save a few grand? Never worth it in the end, when failures plague the operations of the plant.

they added a bunch of machines and we couldnt even power them up because the service was too small. now that they got the new service they can do whatever they want now.

 

[electricalperson]

Here is another key phrase I missed the first time I read the post. "as requested by the owner and architect to be reused".

Makes you wonder which one of them did the load calculation and inspected the panel for serviceabilty. They really should pay either the contractor or an engineer to do a load calculation.

You see a lot of this sort of thing where the owner or architect try to make important decisions about the electrical system and you couldn't find two people less qualified. Normally neither the owner or architect has had any electrical training.

architects are pains. only thing there good for is where to put the tv and the couch in the big living room. they should not be talking about electrical installations.

 

[benaround]

It doesn't help any that 500MCM is rated for 380a and the load is 385a +, IMO, this is

not even a NEC compliant installation.

 

[buzzbar]

I'll ask again. What is ACTUALLY humming? Is the breaker vibrating? Is the lug vibrating? I think that we can all agree it's humming because of an overloaded panel or circuit, but what is physically happening when the hum occurs?

Thanks guys.

 

[charlietuna]

Ever feel 500 MCM with 385 amps flowing thru it? Believe me, it's "HUMMING"! And probably the breakers are adding to the vibration..

 

[realolman]

I am willing to be that if an NEC load calculation is done it will indicate that the loads served by this panel need a supply ampacity of greater then 600 amps.

If the actual load is hitting 385 amps I would be very surprised if NEC load calcs would even allow a 600 amp supply. (The existing 400 amp and the proposed 200 amp panels)

If I was the owner, I'd be wondering how I ended up with this after paying all the architects, contractors, inspectors, and fees.

How did this happen?

We can gripe about owners all we want, but ultimately, they are not the ones responsible.

 

[realolman]

I'll ask again. What is ACTUALLY humming? Is the breaker vibrating? Is the lug vibrating? I think that we can all agree it's humming because of an overloaded panel or circuit, but what is physically happening when the hum occurs?

Thanks guys.

I don't know, but I'm gonna take a WAG.
When current flows through a conductor, it causes a force perpendicular to the wire. I suppose that force could cause the conductor to move enough to cause a sound... But again that's just a WAG... I really don't know.

 

[nakulak]

your science project

your science project

I'll ask again. What is ACTUALLY humming? Is the breaker vibrating? Is the lug vibrating? I think that we can all agree it's humming because of an overloaded panel or circuit, but what is physically happening when the hum occurs?

Thanks guys.

I think it would make a great video if someone were to take a couple of breakers partiallly apart and put a camera and mike on them while tracing up the current curve till they trip (so you could see the little parts inside humming ?) (I wonder if someone already has a video of that ?)

 

[ksmith846]

I'll ask again. What is ACTUALLY humming? Is the breaker vibrating? Is the lug vibrating? I think that we can all agree it's humming because of an overloaded panel or circuit, but what is physically happening when the hum occurs?

Thanks guys.

Feeders were humming

 

[ksmith846]

It doesn't help any that 500MCM is rated for 380a and the load is 385a +, IMO, this is

not even a NEC compliant installation.

240.6 next breaker size up is 400.....this is typical

 

[ksmith846]

Update on what we have done..........first of all the Engineer....in my opinion did not calculate the loads correctly......second we have temporarily tapped a new 200 amp Panel to the Transfer Switch within 10 feet........next we are in the Process of permitting and installing a new 400 amp service to relocate about 200 amps of load to.

We also replaced the 400 amp main and re-torqued all lugs etc.

 

[ksmith846]

If I was the owner, I'd be wondering how I ended up with this after paying all the architects, contractors, inspectors, and fees.

How did this happen?

We can gripe about owners all we want, but ultimately, they are not the ones responsible.

I did not gripe about the owner......although in today's economy the cheapest GC gets the job and they always want to VE the job however possible to maintain their edge (not right I know,but this is how it is). I told them from the begining that the service was too small and the existing Panels should be replaced.

Engineer's original drawing for bid showed the following:
(2) separate 400 amp services (Meters and Main Dsiconnects) both feeding into one 1000 amp Manual Transfer Switch then from there running 2 sets of #500 KCMIL 50 feet each to MDP's "A" and "B"

With this in mind...I wonder how they screwed up the load calculation??
Owner wants cheapest job possible + Contractors/Engineers willing to do whatever it takes to get the job = TROUBLE....

So I guess the Owner has to have some of the responsiblity here.

 

[charlietuna]

Ksmith,
I agree with your therory "not to make waves" because in the end, most owners get upset with the party telling them the bad news, that they got screwed, rather than the party who was responsible. And then the engineering firm's relationship is lost as the owner tells them what the REAL problem is. Of course the engineering firm will tell the owner that you are "ONLY" an electrical contractor and poorly educated and don't know what you are talking about--AND THE OWNER WILL BELIEVE THEM! I have been through this situation many times. Better to keep your mouth shut and do the extra work as the engineering firm covers up their mistakes!

 

[ohm]

Ksmith,
I agree with your therory "not to make waves" because in the end, most owners get upset with the party telling them the bad news, that they got screwed, rather than the party who was responsible. And then the engineering firm's relationship is lost as the owner tells them what the REAL problem is. Of course the engineering firm will tell the owner that you are "ONLY" an electrical contractor and poorly educated and don't know what you are talking about--AND THE OWNER WILL BELIEVE THEM! I have been through this situation many times. Better to keep your mouth shut and do the extra work as the engineering firm covers up their mistakes!

ditto Charlie

 

[realolman]

With this in mind...I wonder how they screwed up the load calculation??
Owner wants cheapest job possible + Contractors/Engineers willing to do whatever it takes to get the job = TROUBLE....

So I guess the Owner has to have some of the responsiblity here.

I guess my question was how does this pass inspection? What is the inspector looking at when he inspects it? How is the engineer designing it? ... by asking the owner what he wants?

Of course the owner wants the most inexpensive job possible, but I don't think the owner has any authority to specify the size of services or feeders, and has no responsibility for the final product, except to write the check.

I think the engineer , contractor, and inspector have the responsibility.

 

[GUNNING]

Change order time! WOOHOO!

Change order time! WOOHOO!

That is some load. I think we all agree the service is undersized. When I run into this thing on smaller breakers I have found that "exercising" the breaker by switching it on and off will set the contacts better with more surface area. Might try that; but I'm thinking the service is overloaded. Big Time. Have you suggested a retrofit to LED"s? or Electronic ballasts? Time to up sell with that new service!

 

[GUNNING]

Duh Moment.

Duh Moment.

How does it pass inspection? The inspector is looking for correct installation as referenced on the architect or engineer sealed set of prints. It is not the inspectors job to re engineer the job on site. Just make sure that what is being done is up to current codes. How they use the product is the authority of another department. (fire department)
Remember the preamble in the NEC that says that following the NEC might not result in a workable or functional installation?

 

[curt swartz]

240.6 next breaker size up is 400.....this is typical

500kcmil is rated for 380 amps and you are not allowed to exceed this ampacity. 240.4(B) allows the overcurrent device to be the next standard size but this does not change the ampacity of the conductors.

 

[danickstr]

I wonder if the humming is the huge number of electrons going through such a relatively small wire. I guess an engineer would know.

 

[iwire]

If I was the owner, I'd be wondering how I ended up with this after paying all the architects, contractors, inspectors, and fees.

How did this happen?

We can gripe about owners all we want, but ultimately, they are not the ones responsible.

Sorry I missed your post, I agree with you entirely.