9 May 2026

Grazing focus: Keeping enough ‘spark’ in your electric fence

With the grazing season now in full swing, Teagasc Beef Specialist, Catherine Egan shares some essential reading and some areas to troubleshoot if your fencer isn’t working as it should.

On many farms, a mains fencer is used on the home block and perhaps battery or solar options are used on outblocks if there is no electricity available. When selecting a fencer, also choose one with a capacity greater than the area needed to be fenced to ensure that adequate power is supplied. There are many benefits of each fencer type, as outlined in table 1 below.

Table 1: Installation, use and key benefits with mains, battery and solar fences

	Mains	Battery	Solar
Installation	Easy-medium	Simple	Medium
Use	Perimeter of farm Temporary fencing	Strip grazing	Temporary fencing Temporary fencing on out farm
Key benefits	Longevity if maintained correctly Suitable for larger areas Greater strength	Easy to install Relatively inexpensive Greatest flexibility and portability	Easy to install Suitable when no power source on farm No re-charging of battery
Caution	Dependent on electricity supply	Risk of theft Battery recharged regularly	Risk of theft Maintenance over winter

What size fencer?

Fencers are mainly advertised in terms of output joules and stored joules. Don’t get these confused and be aware of which is on the charger. A charger may advertise 30 joules but only refer to the stored joules (a fence charger will always store more joules than it outputs). Stored joules represent the amount of power stored inside your charger. This is ran through an output transformer, which converts the power to a higher voltage. Some of the power is lost during this conversion.

Output joules refer to the actual output of the charger – the power available to shock the animal. The size of fencer depends on the area to be fenced. Always choose a fencer to match the area. It is better to choose a fencer greater than your requirement rather than less than recommended and expect it to cover more area than advertised.

Table 2: A guide to mains fencer output and area covered

Output joule	Distance (km)	Area (acres)	Earthing rods
0.12	1.5	4	1
1	1.6	10	1
1.10	10	30	2
2.5	11	50	1-2
3.3	15	50	3
4.9	22	75	4
6.1	32	110	4
7	32	100	3
15	72	200	5
33	145	300	6

Note: This is a guide. Always read and follow the manufacturer’s guidelines

Battery fencers

Battery fencers are used for short or temporary fences where portability and flexibility are the main considerations. A dry battery is used in many cases. While a wet 12V Battery allows rechargeable batteries to be used and facilitates a more powerful battery powered fencer.

Table 3: A guide to battery fencer output and area covered

Output joule	Distance (km)	Area (acres)	Earthing rods	Recommended use
0.2	1.5	4	1	Strip grazing
0.35	4	12	1	Small/medium area
0.43	5	14	1	Medium area / strip grazing
1	8	25	2	Small/medium area
2	11	40	1-2	Medium/large area

Note: This is a guide. Always read and follow manufacturer’s guidelines

For further insights, view the Teagasc Beef Farm Infrastructure Book here (PDF).