# How do you calculate GMD?

## How do you calculate GMD?

Then GMD, now called mutual GMD is approximately =[D1D2D3]^(1/3) and GMR, now called Self GMD => is to be calculated for each group of conductors of each phase separately as Ds1, Ds2 and Ds3 and the the geometric mean taken, Then the self GMD, Ds=[Ds1 Ds2 Ds3]^(1/3).

What is the suggested conductor sizing principle by the NEC concerning load reduction?

The minimum feeder circuit conductor size, without the application of any adjustment or correction factors, shall have an allowable ampacity equal to or greater than the noncontinuous load plus 125 percent of the continuous load.

### When conductors in vertical raceways must be supported one cable support shall be provided _____?

At least one support method shall be provided for each conductor at the top of the vertical raceway or as close to the top as practical. Intermediate supports shall be provided as necessary to limit supported conductor lengths to not greater than those values specified in Table 300.19(A).

What is geometric distance?

GMD stands for Geometrical Mean Distance. It is the equivalent distance between conductors. GMD depends only upon the spacing. GMD comes into the picture when there are two or more conductors per phase.

## Is Geometric Mean distance GMD the same as Geometric Mean radius GMR?

GMD stands for Geometrical Mean Distance. It is the equivalent distance between conductors. GMD comes into the picture when there are two or more conductors per phase used as in bundled conductors. GMR stands for Geometric mean Radius.

Because the load will continue for three hours or more, this branch circuit is considered a continuous load. Therefore, multiply the load by 125 percent (13.6 × 125% = 17).

### When sizing conductors used to serve electric heat branch circuit conductors must be sized at?

When sizing branch-circuit conductors, the minimum branch-circuit conductor size shall have an allowable ampacity not less than 125 percent of the continuous load [210.19(A)(1)]. When sizing overcurrent protection, the overcurrent device rating shall not be less than 125 percent of the continuous load [210.20(A)].

How far apart should conduit be supported?

PVC must be supported every 3 ft. for trade sizes ½ inch through 1 inch. The support distance increases as the conduit size gets larger. For example, 2 inch PVC conduit can be supported every 5 ft; 6 inch PVC conduit can be supported every 8 ft.

## What is the maximum spacing for supporting a 250 Kcmil copper conductor in a vertical Raceway?

10 feet
Note: Beginning with the 2014 National Electrical Code (NEC), article 330.30(B) allows for listed MC Cables (including Riser MCTM High Rise Cable) with ungrounded conductors 250kcmil and larger to be secured at intervals not exceeding 10 feet in vertical installations.

What is the geometric mean distance of a cable?

Where the spacing varies between cores (for example in flat configurations), an average spacing is used; the geometric mean distance. Given known spacing between conductors, the geometric mean distance is given by: The spacing between cores depends on the cable arrangement and configuration.

### What is the geometric mean radius of a conductor?

geometric mean radius is the same as the radius of the centre of the conductor will give exactly the same inductance value as two axially offset ﬁlaments. (We are assuming conductors of round cross section.)

What is the geometric mean distance used for?

This is particularly obvious in the calculation of inductance. Where the spacing varies between cores (for example in flat configurations), an average spacing is used; the geometric mean distance. Given known spacing between conductors, the geometric mean distance is given by:

## How to calculate the inductance of rectangular conductors?

A number of approximate equations exist for calculating the inductance of rectangular ~onductors [1-5].1 The usual method is to calculate the mutual inductance between two fila­ ments spaced a distance apart equal to the geometric-mean-distance [6] of the conductor or conductors.