Voltage Drop Formula

In the PANEL? Usually VD is only an issue in the conductors when the length is long. There is very little VD in a switchgear busbar system that is properly designed and maintained.

yes, that will be very low, but one of my client is asking for that, so can u just tel me how to calculate that? is thr any formula for that?

The Standard VD formula applies. Even though your customer is asking for the VD in a LV panel. The formula stays the same. Calculate the length of the busbars in your LV panel. Apply the VD formula and you will see very negligible VD. Good Luck!

Your client must be in ownership or management, which would explain this weird question.

Tornado's (#4) response is valid. A little research and you'll have the basic VD formula. Remember, the formula is for VD period! Whether you are applying it to an LV Switchgear panel or a legitimate length of a Conductor wire. You are getting closer to the answer...(lol).

VD = √3 X V X I X L X COS Ǿ, this is the formula know?

Once again, British Standard 7671 gives all.

Tinoj,

I suspect the question you have asked is not the question you need answered. In a panelboard, the busbars and conductors all have a precise resistance, based on their dimensions and the resistivity of the metals (typically copper or aluminum). The voltage drop on these components is then fairly easily calculated by the application of Ohm's law, E=IR. This formula works for nearly all parts you are interested in.

However, I believe the question that is of greatest concern is whether your panelboard has too high a voltage drop due to components that have poor connections. If you know the predicted voltage drop of all the components, and compare it against the actual voltage drop, this might suggest that one or more connection(s) are bad, but it might also suggest that your original calculation was bad. Typically bad connections have too high a resistance and therefore cause localized heating. It is this heating which is your problem. Uncorrected, it can lead to equipment failure and fires. The most reliable way to detect this is with an infrared camera in the hands of a skilled operator.

Measuring voltage drops requires you to be "hands-on" with a panelboard that is open. Doing an infrared scan may require the covers to be off, but doesn't involve putting any leads or probes directly into the works.

Hope this helps--JMM

Thank you Mr. Jmuller,

this explanation is good. It helps me a lot. Once more thank you so much.

Unless there are loose, corroded, or otherwise bad connections within the panel, the voltage drop there will be insignificant. I suspect that the real question is how much voltage drop there is in the wiring from the panel to the loads it serves. This latter is a common issue, which depends on the wiring size and length, and whether single or 3-phase.