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The table below helps you select the correct gauge of wire for your loop amplifier. The type of wire is not too important, though experience has shown that a stranded cable with tri-rated insulation is probably the easiest to install and most robust in use. So for example, an ILD122 amplifier when using a 1.5mm² loop cable, will work with a minimum length down to 17m and a maximum length of up to 90m. Any length in-between these two values should work fine though beware of working right at the limits of cable size. If in doubt, use a different size of cable such that the total loop length is well within the minimum and maximum lengths.

Cable / Wire DataILD20ILD122ILD252 (USA)ILD9
Length (m)Length (m)Length (m)Length (m)

Resistance|Z| @MinMaxMinMaxMinMaxMinMax
Ω per1.6 KHzDC1.6 KHzDC1.6 KHzDC1.6 KHzDC1.6 KHz
FB 1.8*0.2920.9580.015021100211333118142250
AWG wireΩ/100ftLength (ft)Length (ft)Length (ft)Length (ft)
22 7×301.4824.8611.6031367131252016927234
20 7×280.9333.0621.11721107211793224343336
18 16×300.6482.1270.89231154312244630462420
16 26×300.3991.3090.706502515028375384100531
14 41×300.2530.8300.6077939579330119447158618
12 65×300.1600.5230.574XX125348188472251653
10 65×280.1010.3300.561XX199357298483398669
FB 1.8*0.2920.9580.4586934369437103592137819
Cable / Wire DataILD100ILD300ILD500
Length (m)Length (m)Length (m)

Resistance|Z| @MinMaxMinMaxMinMax
Ω per1.6 KHzDC1.6 KHzDC1.6 KHzDC1.6 KHz
FB 1.8*0.2920.9580.01502160218731147
AWG wireΩ/100ftLength (ft)Length (ft)Length (ft)
22 7×301.4824.8611.6031354138120135
20 7×280.9333.0621.11721812111632197
18 16×300.6482.1270.892311013114646247
16 26×300.3991.3090.706501285018475312
14 41×300.2530.8300.6077914879214119363
12 65×300.1600.5230.574XX125226188383
10 65×280.1010.3300.561XX199232298392
FB 1.8*0.2920.9580.4586919769284103481


* FB 1.8 is Flat Copper Tape

Table Notes

The table above gives comprehensive information on the minimum and maximum length of cable of a particular wire gauge that can be used with specific Ampetronic loop drivers. Each driver has a specified minimum resistance and maximum impedance at 1.6KHz which can be driven at full current.

Feeder Cable

The values given in the table ignore the resistance of the feeder cable (the cable connecting the loop to the loop driver) which is normally very low. If the situation is marginal, or where very long feeder cables are involved, additional design must be done to compensate. Feeder cable should always be tightly twisted to ensure that the reactive component is very low resulting in a low magnetic field near to the equipment. Use of shielded cable has no real advantages as magnetic radiation is not affected. Parallel wire cable (eg Fig 8) as used by some loudspeaker manufacturers is not recommended. Very often, the wire gauge of the feeder will be similar to the actual loop cable.

The actual feeder length is double the physical length for resistance (send and return). This is important when calculating the total resistance of the system.

Star Quad Feeder Cables

For very long feeder cables, the recommendation is to use a 4-core round cable in a “star quad” configuration. Optimum cable size is 1.5mm² / 2.5mm² (14AWG / 16AWG). The opposing cores are connected together, providing a very low resistance and inductance with little magnetic radiation. This style of cable is often used for 3-phase + earth power connection of machinery.

UK style is 3184Y, harmonised H05VV-F. Similar UL approved cable is SV-3, UL recognised 4097. Total resistance of 100m of 3184Y cable, 2.5mm² per core is 0.69Ω (4-core 14AWG cable is 0.252Ω/100ft). This is well inside the capabilities of the Ampetronic loop drivers.

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