The Live Front vs. Dead Front Bushing

Live front bushings on a pad mount transformer

Today, I’ll give you a quick rundown on the difference between live front bushings and dead front bushings. Before we dive in, if you need to brush up on how transformers work, I recommend you check out our comprehensive guide to electrical transformers.

What is a transformer bushing?

A transformer bushing is an insulator that allows a conductor to pass safely through the tank wall of a transformer without making electrical contact with it.

What is a live front bushing?

It’s called live because the terminal is actually exposed. There is electricity flowing through it. Touching a live front bushing could result in electrocution. As a matter of fact, you don’t want to even get too near due to arc-flash concerns.

Parts of a transformer live front bushing

The bushing itself has several components. A spade is at the top of the bushing. This is the place where the actual termination is made with a mechanical lug or a crimp lug. Below the spade are the bushings made up of little ridges called waffles or sheds. These waffles help protect against something called creep. Creep is where a tiny arc travels across a surface area by “creeping” along with some small amount of water, dust, or oil. Waffles provide the necessary clearance to prevent creep by providing a larger amount of surface area. Finally, there is a stud where the bushing internally connects to the core and coil.

What is a dead front bushing?

The majority of padmount transformers these days come with dead front bushings. These do the exact same thing as a live front bushing but it uses a fully insulated bushing. The obvious benefit is that you can open the cabinet and there is a very low risk of arc-flash. The fully rubber dead front bushing is terminated using a loadbreak elbow.

Both options have suitable applications.

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