Neutral to ground bypass capacitor

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Mintsk8er
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Neutral to ground bypass capacitor

Post by Mintsk8er » Thu Sep 15, 2022 2:28 pm

I'm about to recap my classic 30 combo (~1997) and ran into another potential issue that I didn't know about. I read a post (not here) which explains how an X2 type safety capacitor (which is designed to fail closed) is connecting between neutral and ground on the power cord side of the transformer. From what I understand, the proper safety capacitor between the neutral wire and ground should be a Y type, which fails open. So, it seems that if the X2 safety capacitor between neutral and ground were to fail then there could be a situation where the mains voltage would connect directly to the chassis, correct?

I don't want to assume I'm an expert on this as I am certainly not, but I am curious about it as I have seen others indicate this as a potential safety issue and possibly a design flaw, to the point where I have heard people say removing the X2 safety capacitor from neutral to ground is best.

Can anyone provide insight on this?

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JamesPaul
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Re: Neutral to ground bypass capacitor

Post by JamesPaul » Fri Sep 16, 2022 3:50 am

Welcome to the forum.

This is not my area of expertise, but I will share what theory I remember.

Capacitors on the mains lines are used for EMI and RFI filtering. The issue is if these capicitors should fail there could be an electrical shock hazard in the device being powered. Safety capacitors were designed to fail in a specific mode, so there is no a risk of electrical shock.

As you have already noted, if the RFI filtering capacitor between neutral and ground fails in a short, the mains are connected to the ground/chassis. This could lead to a fatal electric shock. For this applicaion the Y safety capacitor was designed to fail open. So if it fails the device loses RFI filtering, and it suffers from noise and interference, but no one dies if they contact the chassis or former ground.

The X safety capacitor replacing the hot-to-neutral EMI filtering capacitor is designed to fail in a short. This is so the inductive over-voltage spike increases the current, which will blow the fuse removing power from the device. There is no shock hazard if there is no voltage in the device.

If there truly is an X safety capacitor between neutral and ground, that does also seem wrong to me.

My insight would be, I think you are hearing people say to removing the X safety capacitor is best becuase removal may increase noise, but it eliminates the chassis shock hazard.

This truly is dangerous stuff, so ensure you fully research it before taking any action and stay safe.
Enzo wrote:I find if the amp is working, that is a good point to stop fixing it.
James Paul's Peaveys
Decade, Classics, Ecoustic, Windsors, VYPYR, Triple XXX, XXL, VKs, Bandit, JSXs, VIP, Piranha and a Penta.

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Pappy B
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Re: Neutral to ground bypass capacitor

Post by Pappy B » Fri Sep 16, 2022 9:14 am

If you go to "justradios.com" they have a lot of information on capacitors including Y and X capacitors.
The more I learn the more I realize how much I don't know.

Mintsk8er
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Re: Neutral to ground bypass capacitor

Post by Mintsk8er » Fri Sep 16, 2022 11:53 am

JamesPaul wrote:
Fri Sep 16, 2022 3:50 am
Welcome to the forum.

This is not my area of expertise, but I will share what theory I remember.

Capacitors on the mains lines are used for EMI and RFI filtering. The issue is if these capicitors should fail there could be an electrical shock hazard in the device being powered. Safety capacitors were designed to fail in a specific mode, so there is no a risk of electrical shock.

As you have already noted, if the RFI filtering capacitor between neutral and ground fails in a short, the mains are connected to the ground/chassis. This could lead to a fatal electric shock. For this applicaion the Y safety capacitor was designed to fail open. So if it fails the device loses RFI filtering, and it suffers from noise and interference, but no one dies if they contact the chassis or former ground.

The X safety capacitor replacing the hot-to-neutral EMI filtering capacitor is designed to fail in a short. This is so the inductive over-voltage spike increases the current, which will blow the fuse removing power from the device. There is no shock hazard if there is no voltage in the device.

If there truly is an X safety capacitor between neutral and ground, that does also seem wrong to me.

My insight would be, I think you are hearing people say to removing the X safety capacitor is best becuase removal may increase noise, but it eliminates the chassis shock hazard.

This truly is dangerous stuff, so ensure you fully research it before taking any action and stay safe.
Thank you for the warm welcome! I appreciate the time you took to respond.

The recap kit that I ordered supposedly includes replacement caps to correct the safety risk involving the X type cap connecting neutral to ground. I attempted to ask the seller about what type of caps the replacements were, but they didn't seem to want to indicate beyond assuring me that the kit includes replacement filter caps for both positions, and simply advised that I wait for the package and read the supplied instructions. I'm not sure why they didn't want to directly respond to my question, but I'll give them the benefit of the doubt for now that they may not have had the info at the time and simply wanted to trust the product that they've been selling for a while now - I guess that's fine with me.

What you described about potentially increasing noise at the "expense" of removal of the neutral to ground cap is about what I figured. And it makes sense to me that the X type should go between line and neutral to work in conjunction with the fuse.

Of course, I'd like to avoid increasing noise if possible. I'm curious if the recap kit supplies a Y type cap as a replacement, and if so, I'll likely replace the corresponding existing X type with that. Although, as you said this is dangerous stuff, so I'll continue my research to be sure.
Pappy B wrote:
Fri Sep 16, 2022 9:14 am
If you go to "justradios.com" they have a lot of information on capacitors including Y and X capacitors.
Thanks! I'll check that out as well.

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JamesPaul
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Re: Neutral to ground bypass capacitor

Post by JamesPaul » Sat Sep 17, 2022 12:04 am

Mintsk8er wrote:
Fri Sep 16, 2022 11:53 am

Thank you for the warm welcome! I appreciate the time you took to respond.

The recap kit that I ordered supposedly includes replacement caps to correct the safety risk involving the X type cap connecting neutral to ground. I attempted to ask the seller about what type of caps the replacements were, but they didn't seem to want to indicate beyond assuring me that the kit includes replacement filter caps for both positions, and simply advised that I wait for the package and read the supplied instructions. I'm not sure why they didn't want to directly respond to my question, but I'll give them the benefit of the doubt for now that they may not have had the info at the time and simply wanted to trust the product that they've been selling for a while now - I guess that's fine with me.

What you described about potentially increasing noise at the "expense" of removal of the neutral to ground cap is about what I figured. And it makes sense to me that the X type should go between line and neutral to work in conjunction with the fuse.

Of course, I'd like to avoid increasing noise if possible. I'm curious if the recap kit supplies a Y type cap as a replacement, and if so, I'll likely replace the corresponding existing X type with that. Although, as you said this is dangerous stuff, so I'll continue my research to be sure.
Pappy B wrote:
Fri Sep 16, 2022 9:14 am
If you go to "justradios.com" they have a lot of information on capacitors including Y and X capacitors.
Thanks! I'll check that out as well.
It is great to see new members joining the forum. It got quiet around here during the pandemic.

Some sellers get into so many different products, they do not track or remember the details on all of them. Likely nothing intentional on their part. At this point in time one can Google the manufacturer and numbers on most parts, and be able to pull up the data sheet or specifications.

I am going to review the justradios.com site myself.

I hope your recap goes well! The C30 is a great amplifier.
Enzo wrote:I find if the amp is working, that is a good point to stop fixing it.
James Paul's Peaveys
Decade, Classics, Ecoustic, Windsors, VYPYR, Triple XXX, XXL, VKs, Bandit, JSXs, VIP, Piranha and a Penta.

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