feeder voltage drop

[rickdaddis@gmail.com]

we are installing an mdp 500' from the source, then we are installing feeders to a 225a mlo 480v panel 200' from the mdp. the engineer is including the 500' in his voltage drop calculation for the feeder from the mdp to the 225a panel, instead of from the mdp to panel. he has us installing parellel 400mcm. is this correct? do we need to include the 500' measurment in the calculation? thank you

 

[Ingenieur]

Yes
it's total voltage drop

 

[iwire]

we are installing an mdp 500' from the source, then we are installing feeders to a 225a mlo 480v panel 200' from the mdp. the engineer is including the 500' in his voltage drop calculation for the feeder from the mdp to the 225a panel, instead of from the mdp to panel. he has us installing parellel 400mcm. is this correct? do we need to include the 500' measurment in the calculation? thank you

Need to? Well the NEC allows you to ignore voltage drop entirely.

That said if you care about voltage drop you need to include the entire circuits.

 

[ptonsparky]

When you have an engineer including it, install as he wants and go on with your day.

 

[iwire]

When you have an engineer including it, install as he wants and go on with your day.

I agree 100%, the customer hired the engineer for a reason. Let the engineer do their job and you make money doing yours.

 

[Smart $]

Recommendation is 5% total drop for feeder and branch circuits. Service conductors are not included in that recommendation.

IIRC the ANSI nominal service voltage within tolerance is when measured at the service disconnecting means... so voltage drop is already considered where that standard is maintained when loaded.

 

[Ingenieur]

A typical service is not 500'
and most utilities undersize the drop
although not required it is good practice/due diligence to consider it
follow the engineers design or own the consequences

he said the mdp is 500' from the 'source' not service
we can assume since mdp source = service
but clarification may be required

we do not have enough info
load profile
load ratios
etc
the engineer who sized it most likely does

 

[Smart $]

...
we do not have enough info
load profile
load ratios
etc
the engineer who sized it most likely does

I agree.

 

[Ingenieur]

200'
225 A
1-400
0.77%

2-400
<0.4%

something doesn't add up
need to see the system and calcs

 

[Smart $]

200'
225 A
1-400
0.77%

2-400
<0.4%

something doesn't add up
need to see the system and calcs

Aluminum, perhaps?

 

[iwire]

something doesn't add up
need to see the system and calcs

Not really, you are not the jobs engineer.

 

[Ingenieur]

Not really, you are not the jobs engineer.

a good engineer always likes to have his work reviewed :happyyes:

 

[iwire]

a good engineer always likes to have his work reviewed :happyyes:

:lol::lol::lol:

I had no idea you do a stand up routine.

 

[rickdaddis@gmail.com]

feeder voltage drop

Aluminum, perhaps?

the mdp is being fed from a 3000a switchboard with a 800a breaker, with parallel 500's, i assumed that the feeder to the mdp (that is feeding 3- 480 v panels on different floors) that is 500' away, would be a separate voltage drop calculation, than the feeders from the mdp to the panels. so if i understand it correctly, for the voltage drop calculation for each panel feed, i have to include the 500' measurement. thank you

 

[topgone]

the mdp is being fed from a 3000a switchboard with a 800a breaker, with parallel 500's, i assumed that the feeder to the mdp (that is feeding 3- 480 v panels on different floors) that is 500' away, would be a separate voltage drop calculation, than the feeders from the mdp to the panels. so if i understand it correctly, for the voltage drop calculation for each panel feed, i have to include the 500' measurement. thank you

Which section are you really involved with?
IMO, measure the voltage at the point where you intend to connect your conductors from and compute for the voltage drop on the line you are trying to install, based on the expected load of the line.

 

[Smart $]

... so if i understand it correctly, for the voltage drop calculation for each panel feed, i have to include the 500' measurement. thank you

Well, it depends on the allowable voltage drop stated in the job spec's or imposed internally by the engineering department and whether there are any other conditions. Other than a couple special case situations, voltage drop mentioned in the NEC is just a recommendation.

As mentioned in earlier posts, it doesn't hurt to "review" the engineering, but unless you discover a noteworthy issue, install the feeders as specified.

 

[Julius Right]

In my opinion, the voltage drop it has to be connected with the minimum allowable voltage at the terminals of a motor or lighting bulb or else. This calculation starts with the minimum supplied voltage at service-see ANSI 84.1 Voltage Range and then continue with the feeder , the branch and the individual circuit voltage drop .
For induction motor minimum allowable voltage see NEMA MG-1- at start and at steady state.
A voltage dip at start it could be 10-20% of motor rated voltage- usually -and 5% at steady state.
If you would know the supply transformer data you could introduce the voltage drop through transformer also. In a more detailed calculation you can start even from the supply grid[system].