Resistance

With either electronarcosis or electrocution, the overall resistance to current flow is due to two factors; the tissues of the body and also the contact between the electrodes and the skin. It is important to keep the resistance as low as possible to maximise the flow of current. It is not possible to alter the resistance of the tissues of an animal, however, it is possible to minimise the contact resistance by applying electrodes in the correct position and maintaining constant pressure during the duration of the stun.

Very often there is a build-up of grease and dirt on the electrodes, especially where localised heating occurs. This build-up has a high electrical resistance and must be regularly removed. Failure to clean electrodes will lead to corrosion, further increasing resistance. Although resistance falls once the current begins to flow, it is the initial resistance that must be overcome to deliver the recommended current in order to produce an immediate stun.

Table 5 shows the typical electrical resistance of animals during stunning. If electrodes are clean and well maintained, and the contact sites have been wetted, then the resistance will be at the lower end of the range. However, if the electrodes are dirty and dry, resistance may be even greater than the ranges in the table.

Table 5 Approximate electrical resistance of animals to stunning current

Species

Electrode Position

Resistance (Ohms)

Pigs (approx. 100kg)

Across the head

150-350

 

Sheep

Across the head, light fleece cover

150-400

Across the head, heavy fleece cover

150-1000

Cattle

Nose to neck

130-230

Table 6 gives examples of currents that may flow, as calculated by Ohm’s Law, and shows whether or not there is enough current to produce an effective stun. It is essential that all electrical stunning equipment displays the voltage and current which flows during each stun cycle. This display must be visible to the operator.

Table 6 Examples of calculating current with Ohm’s Law

Species

Voltage (V)

Resistance (Ω)

Current (A)

Effective Stun?

Pig (clean electrodes)

250

150

1.6

Yes

Pig (dirty, worn electrodes)

250

350

0.7

No

Sheep (short, wet fleece)

250

200

1.25

Yes

Sheep (long, dry fleece)

250

1000

0.25

No

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