Is this second TVSS necessary?

[Installer]

I am reviewing a Contract.
We are putting in a new Service (Panel and Disc switch) outside connected to an existing panel 150 feet away inside a small building.

• The existing panel has a TVSS.
• The new panel will feed a sensitive electronics cabinet controlling Fuel.
• The Contract says no TVSS is required within 150' of a panel with an existing TVSS.

I am asking for a second TVSS at the new Service outside.
My reasoning is that if a Lightning surge would hit the new Service, it would damage the Electronics cabinet for the fuel controls before it reaches the TVSS indoors at the existing panel 150' away at the small building.

 

[gar]

190621-2129 EDT

Installer:

Yes put a TVSS at the input of the outside panel. Then put another TVSS at the input of the electronic equipment.

You need to study the V-I characteristic of various kinds of TVSSs, and how this relates to source impedance. Also how explicit filtering can help.

Most TVSSs are not very close clamping devices. The start of their clipping must be some substantial level above the maximum expected normal peak supply voltage. For a 120 V circuit this probably means 135/0.707 = 200 V, possibly a little higher.

.

 

[LarryFine]

I agree. I suspect their 150' distance presumes the existing TVSS is upstream of their controller.

 

[Installer]

So the "Contract" is wrong like I thought ?
The outside TVSS will be a Rayvoss Strikesorb which is a very good brand.
The 150' run will likely be 10 AWG or 8 AWG at 120 VAC 40 A
On Monday I will find out what the existing TVSS model is.
I
.

 

[gar]

190622-0841 EDT

Installer:

Probably typical in its characteristics, which is not very good for real protection of electronic equipment.

No curves were shown and I don't know what is in the UL spec. But my guess is that around 25 kA the clamping voltage is around 600 V. 600/200 = 3 is not good protection of electronic components. Many electronic devices (diodes and transistors) are normally run relatively close to their rated breakdown voltage.

For good protection of electronic equipment there needs to be protection within the equipment. Then the moderately high impedance of the input transformer or other input current limiting elements can work effectively with an internal transient limiter. Anything outside the electronic equipment limiting peak voltage is of course important.

I have a whole house transient limiter. This did not prevent damage to a TV. My GE oven has to have its breaker turned off unless the oven is in use becaise it constantly wants to beep. My GE microwave has problems and randomly goes into crazy states requiring power removal and a reboot on application of power. These pieces of equipment probably have no internal transient limiting and have received damage from line transients.

MY GE RR relays have never suffered any transient damage, no internal electronics. I would not want to build a home or business using solid-state relays for switching for two reasons --- transient voltage failure, and high internal power dissipation (about 1 V and relatively independent of current). An RR relay drop is down in the millivolt range, even at 20 A. For dimming you have to use solid-state or large variable transformers. The transformers are better, but large and expensive.

.

 

[Installer]

190622-0841 EDT

Installer:

Probably typical in its characteristics, which is not very good for real protection of electronic equipment.

No curves were shown and I don't know what is in the UL spec. But my guess is that around 25 kA the clamping voltage is around 600 V. 600/200 = 3 is not good protection of electronic components. Many electronic devices (diodes and transistors) are normally run relatively close to their rated breakdown voltage.

For good protection of electronic equipment there needs to be protection within the equipment. Then the moderately high impedance of the input transformer or other input current limiting elements can work effectively with an internal transient limiter. Anything outside the electronic equipment limiting peak voltage is of course important.

I have a whole house transient limiter. This did not prevent damage to a TV. My GE oven has to have its breaker turned off unless the oven is in use becaise it constantly wants to beep. My GE microwave has problems and randomly goes into crazy states requiring power removal and a reboot on application of power. These pieces of equipment probably have no internal transient limiting and have received damage from line transients.

MY GE RR relays have never suffered any transient damage, no internal electronics. I would not want to build a home or business using solid-state relays for switching for two reasons --- transient voltage failure, and high internal power dissipation (about 1 V and relatively independent of current). An RR relay drop is down in the millivolt range, even at 20 A. For dimming you have to use solid-state or large variable transformers. The transformers are better, but large and expensive.

.

We have good internal surge suppression in the Electronics Cabinet.

• I think its a metal oxide varistor or silicon avalanche diode Switch.

I am wondering whether that is enough to provide protection from a lightning surge .

• Would a TVSS located at the Service to the Cabinet diisapate the Surge from a nearby Lightning strike to the counterpoise faster?

• Would a TVSS be a more "Robust" form of protection.

Finally, if we get a Direct Hit (vice) nearby Hit, is it true nothing will really help?
A direct Lightning strike has thousands of Amps with a nanosecond rise time.

Thank you in advance

 

[ATSman]

In the industry the term TVSS has been replaced with SPD (Surge Protection Device.)

This was an email exchange with myself and two Electrical Consultants (PE's) with many years in the business.
Read from the bottom up.

I can probably dig up some pics I have of blow-ups of ATS units I have worked on if anyone's interestered.

 

[gar]

190622-1502 EDTInstaller:HAAS CNC machines use a 100 ohm 1/4 W carbon composition resistor in series with each RS-232 input. On the HAAS side of the resistor, basically the input to the RS-232 interface chip, is a Transorb (basically two Zener diodes in series opposition) shunting the signal to chassis. All control electronics is referenced to the machine chassis. RS-232 signals are +/-12 V or less. Most input RS-232 chips can tolerate +/- 25 V.I ran a test on an 18 V Transorb fed from a 100 ohm 1/2 W carbon comp. I applied 120 power to this series combination. The carbon comp was blown apart, the Transorb survived with no degradation. When an abnormal ground condition exists, such as a hot short to a chassis, then generally HAAS RS-232 inputs don't fail, yet the interface chips and more in a connected computer likely fail because most computer RS-232 devices don't contain this type of protection .It is all a matter of relative impedances, location, and energy.A series sacrificial element with a suitable clamping element may provide very good protection. .

 

[Installer]

Reading about Lightning right now. Still believe the TVSS is needed at the outdoor service.
Don't think the TVSS at the panel 150' away is going to do anything to protect the 120 VAC electronics in the cabinet from a surge induced by a Lightning strike,
A TVSS at the new outdoor service will detect the rise at the Site and send it to the Counterpoise (4 10' rods 10' apart 4 AWG)

 

[gar]

190622-2230 EDT

Installer:

Suppose your resistance to earth is 10 ohms, many locations it is higher. Suppose a direct lighting strike produces a current of 1000 A, could be much higher. Then the voltage at the grounding rod will rise to 10,000 V relative to remote earth from the current passing to earth.

The service lines rise by this 10,000 V going to the load end and its remote earth connection. Yes, you need the TVSS at the load end. Some of the lightning current may flow on the service neutral, but just the wire is a high impedance to the high frequencies in the lightning current. Put TVSSs at various locations to minimize current and voltage at the load.

.

 

[Installer]

190622-2230 EDT

Installer:

Suppose your resistance to earth is 10 ohms, many locations it is higher. Suppose a direct lighting strike produces a current of 1000 A, could be much higher. Then the voltage at the grounding rod will rise to 10,000 V relative to remote earth from the current passing to earth.

The service lines rise by this 10,000 V going to the load end and its remote earth connection. Yes, you need the TVSS at the load end. Some of the lightning current may flow on the service neutral, but just the wire is a high impedance to the high frequencies in the lightning current. Put TVSSs at various locations to minimize current and voltage at the load.

.

Thanks