# Calculate voltage drop in Revit MEP

• 2009-06-11, 01:48 PM
baji-gal.ferenc
Calculate voltage drop in Revit MEP
I need to calculate voltage drop in Revit MEP. I can see that there is a
possibility the problem is that I don't know what formula Revit uses. I
can't find it in help either. Is there any way to customize voltage drop
calculation ot maybe an option to use different standards?

Thanks for you help,

Frank
• 2009-06-11, 03:11 PM
james.klatt
Re: Calculate voltage drop in Revit MEP
I have created a voltage drop table but it requires some manual entry. I have only developed it up to 1/0 wires and have not used it on an actual project yet and I may not. Just to get it to 1/0 is 90 if/then statements at least. This might be better done in excel and brought in. If you want to try to do it, I can give you some direction but i've spent 40 hrs at least just to get it to where it is now. So be ready to invest some time.
• 2009-06-12, 01:04 PM
mjdanowski
Re: Calculate voltage drop in Revit MEP
After some experimentation, I have concluded that the distance between two circuits (when calculating the length of the circuit) is acquired by adding X+Y+Z distances together.

How voltage drop is actually calculated past that though is a mystery.
• 2009-06-12, 02:57 PM
james.klatt
Re: Calculate voltage drop in Revit MEP
The other big problem I have found with voltage drop and wire size in Revit is that you cannot override wire size. I just don't think Revit is ready for voltage drop or demand loads, just doesn't work.
• 2009-10-14, 02:10 PM
musicjunkie300
Re: Calculate voltage drop in Revit MEP
I've done some other testing regarding voltage drop in MEP. the first thing i did was to write down the existing volate drop, branch circuit length, and wire size for the circuit. Next i added a fixture (with a load of .01VA) to the previous existing circuit (277V for anyone that cares) and placed it approximattley 300' away (making this portion of the circuit easily the furthest run). I went back to the circuit characteristics. The load did only change by .01VA as expected, the length did go up roughly 300', but the wire size and voltage drop went up significantly (from a #8 to a #6 and from 5.5V to 6.5V).

The next part of my test i added another .01VA on a different portion of the circuit (to ensure that this would not make it the longest run).

Again, i went to the circuit properties to see that the length had increased and that the voltage drop increased.

Based on this i feel confident in saying that REVIT does the following to calculate the Voltage drop you see in the circuit properties.

a) it takes the total load on the circuit
b) it adds up the entire length of circuit as if all the fixtures were daisy changed together.
c) it then calculates by assuming you have the total load at the very end of the fixture.

this viloates (2) important aspects to actually calculating voltage drop.

1) that all your fixtures are obviously not daisy changed together.
• 2009-10-14, 03:16 PM
tys90
Re: Calculate voltage drop in Revit MEP

That may or may not answer your question exactly, but it should help.
• 2009-10-14, 03:43 PM
musicjunkie300
Re: Calculate voltage drop in Revit MEP
While the articule does address how Revit approaches calculating voltage. Which i agree with but, I would agrue that how it uses the max amperge at the total branch circuit length rather than longest circuit run makes the calculation done worthless.
• 2009-11-04, 04:12 PM
Glider pilot
Re: Calculate voltage drop in Revit MEP
If its having trouble with simple single phase circuits what sort of problems are you likely to encounter when you get a mixture of single and three pase circuits.

Seems to me that what is required is a link to something like amtech, unless you are planning to develop the same level of sophistication into Revit.

http://www.amtech-power.co.uk/index.htm