Hello Everyone. I figured this would be a good question for the smart grounding and bonding guys. In order for a simple residential power strip with surge protection to work does the receptacle that the strip is plugged into need to have a ground for the surge protection to work ?if so why and really briefly how does surge protection work. Thankyou , how many joules protection should i look for
power strip surge protection
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Re: power strip surge protection
All power strips I know of have MOV's installed in all modes (L-N, L-G, & N-G) so yes a ground is required. Do not skimp on cost or just buy one for the AC plug only if you are using on something with I/O ports. You want something for every type of I/O port you will use like coax and tele-line, RJ-45, etc. Ignore the joule rating it means nothing. Isntead look for a UL-1449 listing of 330V with as large of surge current per mode (10KA min) you can afford. If the unit does not specify these values walk away. A good unit will cost $50+
All power strips I know of have MOV's installed in all modes (L-N, L-G, & N-G) so yes a ground is required. Do not skimp on cost or just buy one for the AC plug only if you are using on something with I/O ports. You want something for every type of I/O port you will use like coax and tele-line, RJ-45, etc. Ignore the joule rating it means nothing. Isntead look for a UL-1449 listing of 330V with as large of surge current per mode (10KA min) you can afford. If the unit does not specify these values walk away. A good unit will cost $50+
LarryFine
Master Electrician Electric Contractor Richmond VA
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- Henrico County, VA
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- Electrical Contractor
Re: power strip surge protection
Bond, surge protection in its simplest form merely redirects electricity over a set voltage to a different pathway to earth, or at least to another conductor. Earth is best, thus, the importance of a good ground.
Bond, surge protection in its simplest form merely redirects electricity over a set voltage to a different pathway to earth, or at least to another conductor. Earth is best, thus, the importance of a good ground.
petersonra
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Re: power strip surge protection
personally, i am suspicious of the protective value of surge protectors in general, and especially the idea that you need a ground for them to work.
take a look at how MOVs work. basically, they are a near short circuit above their clamping voltage, and a near open circuit below that voltage.
usually, a surge protector has protection from L-N, N-G, and L-G. any time you get a voltage between any of the two of the three lines that exceeds the clamp voltage, the MOV turns on and basically shorts out the high voltage. But it does not go to ground. It goes from L-N, L-G, or N-G, depending on which set of lines has a high voltage on it.
if you only have two lines coming in (L and N), the MOV will still operate and reduce the voltage across those two lines.
Since N and G are connected at the service point any way, there should not be a whole lot of voltage across them. It can happen due to the very fast rise time of some transients that you get a high voltage from N-G. But if you are not connected to ground, what difference does it make?
[ July 15, 2005, 07:50 AM: Message edited by: petersonra ]
personally, i am suspicious of the protective value of surge protectors in general, and especially the idea that you need a ground for them to work.
take a look at how MOVs work. basically, they are a near short circuit above their clamping voltage, and a near open circuit below that voltage.
usually, a surge protector has protection from L-N, N-G, and L-G. any time you get a voltage between any of the two of the three lines that exceeds the clamp voltage, the MOV turns on and basically shorts out the high voltage. But it does not go to ground. It goes from L-N, L-G, or N-G, depending on which set of lines has a high voltage on it.
if you only have two lines coming in (L and N), the MOV will still operate and reduce the voltage across those two lines.
Since N and G are connected at the service point any way, there should not be a whole lot of voltage across them. It can happen due to the very fast rise time of some transients that you get a high voltage from N-G. But if you are not connected to ground, what difference does it make?
[ July 15, 2005, 07:50 AM: Message edited by: petersonra ]
Re: power strip surge protection
The SPD's are installed between any two points in a electrical systen to limit voltages. In the case of a power strip, a class "A" device, the SPD's are installed between L-G, L-N, and N-G called modes. If any one of the mode clamping voltage is reached the device operates and limits the voltage. Just because the L-G or N-G mode may operate, no current path is through earth, just the EGC and phase wires.
[ July 15, 2005, 03:44 PM: Message edited by: dereckbc ]
Larry earth has no function or purpose in a TVSS device or its operation. Any SPD (surge protection device like MOV's or SAD's) is passive and only operates when its clamping voltage is reached. When it operates it is a simple clamp or crowbar and absorbs energy just like your screw driver. In other words it becomes a very low impedance load device or short circuit, and sends it right back to the source.
The SPD's are installed between any two points in a electrical systen to limit voltages. In the case of a power strip, a class "A" device, the SPD's are installed between L-G, L-N, and N-G called modes. If any one of the mode clamping voltage is reached the device operates and limits the voltage. Just because the L-G or N-G mode may operate, no current path is through earth, just the EGC and phase wires.
[ July 15, 2005, 03:44 PM: Message edited by: dereckbc ]
Re: power strip surge protection
If you are talking about a grounded service entrance location(class "C" location) where there is a N-G bonded, you are correct. Many TVSS manufactures offer class "C" devices with added L-G, and N-G modes which are a complete waste of material because of the N-G bond at the service.
However once you get downstream from the service entrance point (about 30 to 60 feet) the inductance and capacitance of the cable comes into play and you get ringing effects from a transient that will cause excessive voltages between L-G and N-G. That is why these modes become necessary in class "B" and "A" locations.
Bob you have picked up on a very good point that is missed during the design phase and not fully understood by most.
If you are talking about a grounded service entrance location(class "C" location) where there is a N-G bonded, you are correct. Many TVSS manufactures offer class "C" devices with added L-G, and N-G modes which are a complete waste of material because of the N-G bond at the service.
However once you get downstream from the service entrance point (about 30 to 60 feet) the inductance and capacitance of the cable comes into play and you get ringing effects from a transient that will cause excessive voltages between L-G and N-G. That is why these modes become necessary in class "B" and "A" locations.
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- Bremerton, Washington
Re: power strip surge protection
LarryFine:
As futher proof that a low impedance ground is not required for a TVSS to operate is the 2005 NEC added in Art 285 the ability to use a TVSS on an ungrounded electrical system.
With the bonding jumper at the service, any transient will go back on the neutral rather than earth.
A TVSS takes the surge and sends it back to the source, not to earth.
LarryFine:
As futher proof that a low impedance ground is not required for a TVSS to operate is the 2005 NEC added in Art 285 the ability to use a TVSS on an ungrounded electrical system.
With the bonding jumper at the service, any transient will go back on the neutral rather than earth.
A TVSS takes the surge and sends it back to the source, not to earth.
Re: power strip surge protection
The only reason I can see for an earth ground would be for surges induced from lightning, as earth is its return path. But at the point-of-use, both neutral and ground will get you to earth in a grounded system.
Not sure how much benefit a point of use surge strip would be for a lightning strike. A service mounted TVSS probably has a better (lower impedance) path to the ground electrode to get rid of lightning induced voltages, at least until it burns up.
I think dereckbc provided the answer for why you'd even bother to put MOV's on N-G and L-G.
The only reason I can see for an earth ground would be for surges induced from lightning, as earth is its return path. But at the point-of-use, both neutral and ground will get you to earth in a grounded system.
Not sure how much benefit a point of use surge strip would be for a lightning strike. A service mounted TVSS probably has a better (lower impedance) path to the ground electrode to get rid of lightning induced voltages, at least until it burns up.
I think dereckbc provided the answer for why you'd even bother to put MOV's on N-G and L-G.
petersonra
Senior Member
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- Northern illinois
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Re: power strip surge protection
You seem to be confusing two seperate issues. One is diverting (or attempting to divert) lightning to earth through a lightning protection system. the other is dealing with a high voltage transient from lightning or some other cause.
In the first case, the TVSS has no role. it is not part of the lightning protection system, if there is one installed.
In the second case, the voltage transeient is not shunted anywhere. The MOV senses a high voltage between two points (the metal leads coming out of the MOV). It turns on, becoming a very low impedance as long as the voltage exceeds its clamping voltage. This reduces the voltage across its two leads (remember E=I*R and if R is near zero, E will be as well). The circuit path is always on those two points, and not to ground (unless one of the two points happens to be ground).
You seem to be confusing two seperate issues. One is diverting (or attempting to divert) lightning to earth through a lightning protection system. the other is dealing with a high voltage transient from lightning or some other cause.
In the first case, the TVSS has no role. it is not part of the lightning protection system, if there is one installed.
In the second case, the voltage transeient is not shunted anywhere. The MOV senses a high voltage between two points (the metal leads coming out of the MOV). It turns on, becoming a very low impedance as long as the voltage exceeds its clamping voltage. This reduces the voltage across its two leads (remember E=I*R and if R is near zero, E will be as well). The circuit path is always on those two points, and not to ground (unless one of the two points happens to be ground).
Re: power strip surge protection
In the lightning induced voltage case, what is the voltage relative to? Currents will most likely be induced on all wires, and the voltage will be relative to ground. No ground reference, no voltage detected (at least in theory). However, I think the currents can be so high in these spikes, that the resistance of the wires can cause significant voltage drop which could cause large voltage differences between adjacent wires.
Like you said, the MOV just monitors two wires and shorts them out above a threshold voltage. The source of the voltage isn't really relevant. But I think the MOV will be more effective against lightning iduced surges if one side of it is tied to an earth ground reference
I was pretty much only considering the second case, but trying to separate lightning induced voltage -vs- voltage induced via other ways, such as a HV line falling on the wires.
In the lightning induced voltage case, what is the voltage relative to? Currents will most likely be induced on all wires, and the voltage will be relative to ground. No ground reference, no voltage detected (at least in theory). However, I think the currents can be so high in these spikes, that the resistance of the wires can cause significant voltage drop which could cause large voltage differences between adjacent wires.
Like you said, the MOV just monitors two wires and shorts them out above a threshold voltage. The source of the voltage isn't really relevant. But I think the MOV will be more effective against lightning iduced surges if one side of it is tied to an earth ground reference
Re: power strip surge protection
A lightning induced current produces in the neighborhood of 1000 volt for every 1-foot of cable length regardless of the cable size. This is why TVSS manufactures require TVSS connection leads to be short (IMO useless in most cases, but that is another story). So if a EGC is your ground reference, how long is it and what voltage will be developed?
Not trying to be condescending, but rather get you to start thinking about what you are really trying to do. Is it the voltage with respect to earth, or the voltage between L-G, L-N, and N-G at the plug you are trying to limit?
We are talking about a point of use or class "A" device are we not? If so how are you going to connect to earth? Via EGC?
A lightning induced current produces in the neighborhood of 1000 volt for every 1-foot of cable length regardless of the cable size. This is why TVSS manufactures require TVSS connection leads to be short (IMO useless in most cases, but that is another story). So if a EGC is your ground reference, how long is it and what voltage will be developed?
Not trying to be condescending, but rather get you to start thinking about what you are really trying to do. Is it the voltage with respect to earth, or the voltage between L-G, L-N, and N-G at the plug you are trying to limit?
wizzracing
Member
Re: power strip surge protection
I would get a well made UPS from ACP. They will cover your phone, Cable, Printers, and anything else pluged in to them. They will also include line condtioning.
Yes a ground is needed or the UPS will show a light "System ground not present"
I would forget those strip surge protectors to start with. They can't react fast enough to stop your systems from burning up.
I would get a well made UPS from ACP. They will cover your phone, Cable, Printers, and anything else pluged in to them. They will also include line condtioning.
Yes a ground is needed or the UPS will show a light "System ground not present"
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- Massachusetts
Re: power strip surge protection
First the typical home APC UPS is off line unless the utility power is off, under normal conditions it is no better or worse then surge suppressors.
Surge suppressors are always on line and work immediately.
A large commercial UPS (full conversion) is another story. Those units convert all AC to DC then create a clean true AC sine wave from the DC. With these units there are no surges.
wizz I don't want you to think I am picking on you but I can not agree with your post above.
First the typical home APC UPS is off line unless the utility power is off, under normal conditions it is no better or worse then surge suppressors.
Surge suppressors are always on line and work immediately.
A large commercial UPS (full conversion) is another story. Those units convert all AC to DC then create a clean true AC sine wave from the DC. With these units there are no surges.
physis
Senior Member
Re: power strip surge protection
It is true that a lot of surge suppression components aren't as fast as a lot of surges.
I don't remember what kind of rise times are typical for either the components or surges. I think it gets to be a problem in the nanoseconds range.
Filters using inductors and capacitors are actually more aggressive at higher frequencies.
It is true that a lot of surge suppression components aren't as fast as a lot of surges.
I don't remember what kind of rise times are typical for either the components or surges. I think it gets to be a problem in the nanoseconds range.
Filters using inductors and capacitors are actually more aggressive at higher frequencies.
Re: power strip surge protection
I found my way to the Zero Surge website after discovering that one of the MOVs in my computer's power strip had exploded and burned. They make power strip surge protectors with no MOVs. Is this a sound solution?
I found my way to the Zero Surge website after discovering that one of the MOVs in my computer's power strip had exploded and burned. They make power strip surge protectors with no MOVs. Is this a sound solution?
mdshunk
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Re: power strip surge protection
That zero surge link is just pseudo-technical mumbo-jumbo. I'm surprised that they don't also claim that their unit is mounted on a baseplate of preframulated amulite.
[ August 31, 2005, 11:15 PM: Message edited by: mdshunk ]
That zero surge link is just pseudo-technical mumbo-jumbo. I'm surprised that they don't also claim that their unit is mounted on a baseplate of preframulated amulite.
[ August 31, 2005, 11:15 PM: Message edited by: mdshunk ]
petersonra
Senior Member
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- Northern illinois
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Re: power strip surge protection
anyone that believes they get substantial additional protection for their electronic equipment from a typical surge strip is almost certainly in error.
most modern electronic equipment is quite capable of effectively dealing with the same level of transients the surge strips can, making the surge strips redundant.
anyone that believes they get substantial additional protection for their electronic equipment from a typical surge strip is almost certainly in error.
most modern electronic equipment is quite capable of effectively dealing with the same level of transients the surge strips can, making the surge strips redundant.
Re: power strip surge protection
Thanks for the replies. I agree that the "trash can" metaphor is unfortunate and vague. But I also have to confess that I already took the bait and ordered 2 of them after finding that a couple of my $50 MOV-based power strips looked like this on the inside, yet continued to deliver power.
What sold me were these oscilloscope traces (Brick Wall uses the same design) and the claim that the design essentially offers the same "protection" as MOVs, without self-destructing within a few years. I'm a renter, so I unfortunately I can't install a whole-house arrester at the service entrance. If my electronic equipment is quite capable of effectively dealing with the same level of transients the surge strips can, then will the insides of my computer and home theater equipment eventually look like my old surge suppressors?
Thanks for the replies. I agree that the "trash can" metaphor is unfortunate and vague. But I also have to confess that I already took the bait and ordered 2 of them after finding that a couple of my $50 MOV-based power strips looked like this on the inside, yet continued to deliver power.
What sold me were these oscilloscope traces (Brick Wall uses the same design) and the claim that the design essentially offers the same "protection" as MOVs, without self-destructing within a few years. I'm a renter, so I unfortunately I can't install a whole-house arrester at the service entrance. If my electronic equipment is quite capable of effectively dealing with the same level of transients the surge strips can, then will the insides of my computer and home theater equipment eventually look like my old surge suppressors?
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: power strip surge protection
the reason movs are so popular in surge strips is because they are CHEAP.
I found a warning about varistors published in an old GE varistor handbook. It reads:
"Should the varistor be subjected to surge currents and energy levels in excess of maximum ratings, it may physically fail by package rupture or expulsion of material."
the reason movs are so popular in surge strips is because they are CHEAP.
I found a warning about varistors published in an old GE varistor handbook. It reads:
"Should the varistor be subjected to surge currents and energy levels in excess of maximum ratings, it may physically fail by package rupture or expulsion of material."
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