TVSS Receptacles

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jginter said:
Does anyone know if installing one TVSS receptacle will protect downstream equipment?
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Yes, but not by very much. TVSS works best when there are layers of protection. One on the service gear, one on the breaker panel, and then the receptacle device. The more layers, the better the protection.

And when you're looking at the sizing of the TVSS device ignore the joules rating. Manufacturers manipulate that number in so many ways it's become meaningless. I size the devices based on surge current (kA).

Maybe this link will help.
 
No it will not protect anything downstream, nor offer much protection for the device plugged into it without a service entrance protector installed at the meter or main panel.
 
jginter said:
Does anyone know if installing one TVSS receptacle will protect downstream equipment?
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Protect it from what?

These days, most electronic equipment is relatively immune to the effects of commonly seen transients. The little bit of energy that a TVSS receptacle can absorb may not offer any additional protection to what is plugged into the receptacle because the equipment won't be damaged by the level of energy the TVSS can absorb.

IMHO, mostly these things are snake oil. A serious TVSS installed at the panelboard is a far better choice, and offers some real protection from more serious transients.
 
Mr. Bill said:
Yes, but not by very much. TVSS works best when there are layers of protection. One on the service gear, one on the breaker panel, and then the receptacle device. The more layers, the better the protection.
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And this statement is based on what evidence?

Mr. Bill said:
And when you're looking at the sizing of the TVSS device ignore the joules rating. Manufacturers manipulate that number in so many ways it's become meaningless. I size the devices based on surge current (kA).
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Very true. Especially with smaller TVSS, the ratings tend to be almost meaningless.

<added>
I went to the link you posted. I think most of the advice is bogus. A "good" ground has absolutely nothing to do with how TVSS's work. They work by creating a low impedance path between two conductors. NOTHING is "shunted" to ground.
 
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I'm sorry. I thought you meant downstream to mean anything feed thru the device. If you're talking about daisy chaining the recept to another like GFI recepts are commonly done then no. The additional recepts will not be protected. Anything plugged into the TVSS recept will have minimal protection unless the panels upstream are protected.
 
petersonra said:
.... I went to the link you posted. I think most of the advice is bogus. A "good" ground has absolutely nothing to do with how TVSS's work. They work by creating a low impedance path between two conductors. NOTHING is "shunted" to ground.
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How then do you explain when surge-protected power strips are plugged into GFI-protected receptacles you get a lot of trips? That shunting to ground action causes the GFI to trip out.

We have had several instances where surge power strips caused GFI's to trip on a regular basis. Replacing the GFI outlets did not solve the problem. Only when we had them install a "normal" power strip without surge protection did the false tripping stop..... :-?
 
Tvss

Tvss

It is my understanding that TVSS devices shunt high voltage transients to ground. If that is correct would'nt a TVSS receptacle installed at the beginning of a circuit provide the same protection for the entire circuit as it does at the point where it is installed? I am being asked to install several TVSS receptacles on the same branch circuit and cannot understand how the additional devices on the same circuit offer any more protection.
 
petersonra said:
A "good" ground has absolutely nothing to do with how TVSS's work. They work by creating a low impedance path between two conductors. NOTHING is "shunted" to ground.
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The following is referenced from EC&M.

How does a TVSS work? Since a TVSS is a voltage-sensitive switch, it constantly monitors the AC voltage input and output waveforms. Nothing happens under normal conditions, but when the voltage difference between the power source and the protected line gets high enough, the switch closes and diverts the transient away from the electronic equipment. We often call this switching voltage the clamping voltage of the TVSS. There are three types of TVSSs used in the market today: clamps, crowbars, and hybrids.

Clamps divert the surge to a grounding reference. The voltage waveform appears to cut off where the surge exceeds the rating of the TVSS. The majority of TVSSs purchased today are "clamps." They are quick to respond; however, they can't handle large amounts of surge current.

Crowbars are slow to respond to a surge, but they can handle enormous amounts of surge current. Called crowbars because they exhibit a negative resistance, they have the same effect as "shorting out" two car battery terminals with a crowbar. Unfortunately, relying solely on a crowbar can be hazardous to the electrical system because it's actually shorting the protected AC power conductors to ground.

Hybrids combine the fast response of the clamp with the energy capabilities of the crowbar. You do this with a sophisticated process of internally constructing the two with fuses and current-limiting impedances. This unit is very expensive and requires careful planning to make sure it won't harm equipment powered from AC power lines. But, it's the best of both worlds as far as surge protection goes.
 
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kbsparky said:
How then do you explain when surge-protected power strips are plugged into GFI-protected receptacles you get a lot of trips? That shunting to ground action causes the GFI to trip out.

We have had several instances where surge power strips caused GFI's to trip on a regular basis. Replacing the GFI outlets did not solve the problem. Only when we had them install a "normal" power strip without surge protection did the false tripping stop..... :-?
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The reason the GFCI trips is because there are MOVs L-N, N-G, and L-G. The leakage current through the MOVs is possibly what is tripping the GFCI. It is also entirely possible that a L-G or N-G transient also occurred. The MOV would operate and the current flow in the L and N legs would not be the same, tripping the GFCI.
 
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petersonra said:
The reason the GFCI trips is because there are MOVs L-N, N-G, and L-G. The leakage current through the MOVs is possibly what is tripping the GFCI. It is also entirely possible that a L-G or N-G transient also occurred. The MOV would operate and the current flow in the L and N legs would not be the same, tripping the GFCI.
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One test would be to temporarily use a cheater.
 
brian john said:
Describe please?
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cheater.gif

Be sure the grounding lug doesn't touch the plate screw.
 
petersonra said:
And this statement is based on what evidence?
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IEEE (Emerald Book 1992) recommends that SPDs be coordinated in a staged or cascaded approach.

One SPD at the service entrance can reduce a 20,000V impulse from a lightning strike to about 800V. A second SPD at a branch panel can reduce this down to 100V. IEEE recommends keeping surges to under 330V peaks.

This is just one situation. Every Oneline is different.
 
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