Over Current Protection Devices

There are many considerations when getting a product to market and luckily there are companies like High Tech Design Safety available to help walk you through the process. In the last video we talked about part selection and HTDS CEO, Steve Barcik Amstel talked quite a bit about over current protective devices and today in this video below, he would like to dig a bit deeper.

(Link to video also available here:  https://www.youtube.com/watch?v=xFB7v7R5E2w )

Critical to your product… is the main power coming in… and then the main over current device and how that functions… and then all of the rest of the over current protection on all the other parts and conductors within your equipment. So imagine that you have a big piece of equipment…You have the main power cable coming in. It is going to terminate at the top of an over current protective device, which is typically also a main disconnecting device. So you will have a large circuit breaker and a rotating handle or pull down handle that can act as the disconnecting device. You will need to be sure that this breaker is a UL 489 over current protective device. It is a branch rated device because we are bringing power into your equipment and distributing it through the equipment. It is almost like we are distributing power within a building, but we are actually just distributing it within your equipment. Providing that main power inlet, that main power over current protective device and that disconnecting means, whether those are two separate devices or one contiguous device…it doesn’t matter…be sure that they are rated for that use.

You also want to be sure that those over current protective devices at the inlet have a high enough interrupt capacity. Interrupt capacity is the ability of that breaker to clear a fault. So let’s say it is a very large piece of equipment, like some of the stuff that we do for steel making or oil and gas or other places where there is a lot of fault current available… And with that let’s say that there are 100,000 amps of fault current available on the line coming into your equipment. Now you might not be able to take that because some of the biggest devices that you see are 65,000 amps of fault interruption. In your manuals and your installation documentation, you are going to need to tell whoever that is… that if there is 100,000 amps that can come into your machine, they need to have an upstream breaker that can clear that for you or you need to put 100,000 amp clearing device in your product.

Now let’s say that we are using a 65,000 amp interrupt capacity breaker and there is 50,000 amps available, when that circuit breaker opens it can clear that arc…that 50,000 amp arc can be cleared by that circuit breaker. Another scenario…we are using that same circuit breaker and we are downstream of substation and we have a couple hundred thousand amps of current there…When the breaker, which is rated at 65,000 amps, goes to clear… when it opens it is not going to be able to extinguish that arc. The 200,000 amps is going to jump that gap and you are going to have catastrophic failure. These are all big numbers and they are dramatic which helps to demonstrate the point…however, in most industrial settings, for example the semiconductor industry, you will need to have the ability to clear 10,000 amps of interruption current. The total of current coming in needs to be able to interrupt that 10,000 amps.

GFCI Devices – Ground Fault Circuit Interrupter

There are some other nuances to over current protection that are critical In some cases you might want to use a GFCI device…Perhaps external to your equipment, you have an outlet to plug in test equipment…. You will need to put a ground fault circuit interrupter breaker on that outlet.

If your equipment is in a wet location where there is a lot of water around…water on the ground, water on the people, might be water on the equipment…you will need to use a ground fault circuit interrupter for those circuits.

In some cases, you might choose to make your main over current protective device a GFCI device or for the Japanese market or other markets…it might also be called an earth leakage breaker, an ELB type breaker. We at High Tech Design Safety can help you to determine which of these breakers you will need.

When you are protecting different devices, you need to determine what the device actually is and how it should be protected. Most of your normal circuits in your equipment can use a UL 489 Breaker or further downstream if you are only protecting one device…you can use a UL 1077 breaker.

Protecting a Heating Circuit

Now if you are protecting a heating circuit, we see a lot of the times where the insulation in the heating circuit can break down and cause electrical shock. We recommend using a GFCI device their as well.

Other scenarios like mixing liquid or a heated chemical bath or even heated water baths, we still recommend the GFCI device.


A lot of the times, here at HTDS, Steve and his team get questions about using fuses. Fuses are great, however, there is more burden on the end user and there is also some other documentation burden as the manufacturer. If you are using fuses, you need to put a label next to the fuse saying what kind of fuse it is, what the current rating is, what type of fuse and all the other data needed. You will also have to include this information in your manuals, parts list, etc. If the fuse goes out, then someone will have to go out and get that fuse unless you supply it with a kit as part of the equipment to use as a spare. This becomes more difficult. And sometimes with smaller more compact or lower cost-of-goods products, fuses might make perfect sense.

When you are selecting your over current protective devices, we want to look at what the down stream device is, how much current is upstream, we want to select it so that the equipment can be UL listed or CE marked, and we want to have all of these breakers to coordinate with each other so that we don’t end up with a fault downstream that causes a fire, an electrocution , or any kind of disaster in your equipment. Selecting these devices in such a way that they meet code and meet standards and allow your equipment to be UL listed, CE marked and globally accepted is a big part of what High Tech Design Safety helps companies to do. Let us know if we can help you.