# How is jam ratio calculated?

## How is jam ratio calculated?

JAMB apportions 60% for UTME and only candidates who scored 230 and above are qualified for this mark….

- Five C6 = 3% x 5 = 15%
- Five C5 = 4% x 5 = 20%
- Five C4 = 5% x 5 = 25%
- Five B3 = 6% x 5 = 30%
- Five B2 = 7% x 5 = 35%
- Five A1 = 8% x 5 = 40%

## What is cable jam ratio?

Jamming is the wedging of three or more cables as they are pulled into a conduit. This usually occurs as a result of crossovers when the cables are twisted or are pulled around bends in the conduit. Jam ratio is defined as the ratio of conduit inner diameter (D) to the cable outside diameter (d). Jam Ratio = D/d.

**What is the ratio of conductor to raceway diameter where jamming occurs?**

The two most popular types of PVC are Schedule 40 and ____. Where PVC conduit is connected to a box or enclosure, a ___ is recommended. When pulling three conductors or cables into a raceway, if the ratio of the raceway diameter to the conductor diameter is between 2.8 and 3.2, jamming can occur.

### What increases the flexibility of a wire?

Ultra-Flex Wire Most industrial wire is made up of multiple wire strands, called ‘base strands’, rather than being made of a solid piece of metal. Multiple strands make the wire more flexible, allowing it to bend and flex more easily than solid metal. The finer the base strand, the more flexible the wire.

### How do you calculate tension in cable pull?

P = Tb / r (Formula 6) Where:P. = actual sidewall pressure on cable, lbs./ft. Tb = pulling tension at and of bend, lbs. The maximum allowable pulling tension at bend (Tbm) is the limit that the calculated pulling tension (Tb) should be compared.

**When pulling three conductors or cables into a raceway if the ratio of the raceway diameter to the conductor?**

between 2.8 and 3.2

Informational Note No. 2: When pulling three conductors or cables into a raceway, if the ratio of the raceway (inside diameter) to the conductor or cable (outside diameter) is between 2.8 and 3.2, jamming can occur.

## What is the adjustment factor if you have a group of 22 current carrying conductors?

The Table 310.15(B)(3)(a) adjustment factor for 22 conductors is 45 percent, but this installation meets the stipulations in 310.15(B)(3)(a)(5). Therefore, it is only required to use an adjustment factor of 60 percent.

## How does conductor length affect ampacity?

Skinny wires have a lower allowable current (“ampacity”) than fat wires, due to their greater resistance per unit length, and consequently greater heat generation per unit current. The National Electrical Code (NEC) specifies ampacities for power wiring based on allowable insulation temperature and wire application.

**What is the most flexible electrical wire?**

RVV cables (as the most popular flexible electrical wire cables) are PVC insulated/sheltered cables and sometimes known as “Light PVC” flexible cables.

### When pulling multiple conductors the pulling tension should?

Pulling tensions should be reduced by 20% to 40% when several conductors are being pulled simultaneously (in parallel) since the tension will not be distributed evenly among conductors.

### What is the maximum allowable tension in the cable when pulling?

1,000 pounds

Traditional conservative practices limit the allowable tension of a basket grip to 1,000 pounds. The conductors of the cable are generally the only members that can bear the pulling forces without damage.

**Which factor does not generally influence the resistance of a conductor?**

EXPLANATION: The resistance of a conductor does not depend on Pressure.

## What is a good jam ratio for conduit?

Note that a 1.05 factor is included to estimate the “ovalization” of the conduit at the bend. While the literature is consistent that jamming can occur with a jam ratio around 3, there is inconsistency on the exact range of jam ratios that pose a problem.

## How many conductors needed to jam a raceway?

While jamming can occur when pulling four or more conductors or cables into a raceway, the probability is very low. Click to expand… It appears to apply to 3 conductors of the same size.

**How do you calculate Jam ratio in electrical wiring?**

To figure out your jam ratio, use the following equation: jam ratio equals conduit ID divided by average cable OD. For example: three 1-inch (2.54 cm) cables in a 3-inch (7.62 cm) conduit yields a 3.0 jam ratio. Jamming only occurs within a jam ratio range of 2.7 to 3.1.

### What is the jam-ratio for two conductors in a circuit?

That why for one conductor you’re allowed 53% fill, for two conductors 31% fill and for 3 or more 40% fill. I have not had this problem in the field, but still want to be sure. There is lot of literature available on the internet about jam-ratio. But there are two questions unanswered. 1.