Surge Protector Types: Type 1, Type 2 and Type 3, and Where to Fit Them

The short answer

• Type 1 is for the service entrance, where some lightning current can arrive. Type 2 is the distribution-board device. Type 3 sits close to sensitive equipment. A building often needs more than one.
• Uc must sit above the highest voltage that is normally on the wires. On a 230/400 V supply both 275 V and 385 V devices are common. A Uc that is too low wears the SPD out on ordinary voltage.
• In is the current used for the repeated test. Imax is a higher single-shot figure. Do not compare a 40 kA Imax with a 20 kA In as if they were the same rating.
• Up is the voltage left for the equipment. Lower protects better, and a very low Up still needs the upstream SPD the maker coordinates it with.
• Solar DC needs a PV SPD, with Ucpv above the array’s cold open-circuit voltage. An AC 275 V unit on a string is the wrong part.

What the types are for

A surge is a short spike, from a lightning strike nearby or from switching a large load. It is not a low voltage that lasts all afternoon, and an SPD is not a stabiliser. It clamps the spike and sends the current to earth, then it returns to waiting. The type tells you which test the device passed, and therefore where it belongs.

Type 1 is tested with a 10/350 microsecond current, written Iimp. That long wave is a share of a direct lightning impulse. Fit Type 1 at the origin of the installation when the building has a lightning protection system, or when an overhead line can bring a partial lightning current inside. It is not a lightning rod. A rod, or air terminal, is the metalwork on the roof that intercepts a strike. The SPD is the device on the wires. A building with a rod still needs SPDs, because the strike raises the earth potential and the cables pick up what the rod did not save you from.

Type 2 is tested with an 8/20 microsecond current. That is the induced surge a distribution board actually sees, from a strike that was nearby or from switching. It is the device for a main board and for sub-boards. On a board in Lahore with no lightning rod and a short service, the usual device is a Type 2, not a Type 1 fitted for its own sake.

Type 3 is tested with a combination wave and is built for a low let-through voltage at the equipment. It has a small energy rating. It expects a Type 2 upstream. Used alone at a service entrance, it is destroyed by a surge it was never asked to swallow. Many makers say to add one when the cable from the Type 2 to the equipment is longer than about 10 m, because the voltage can ring up again along a long run. That distance is guidance from manufacturers, not a substitute for the coordination distances in the manual of the devices you are fitting.

The Phoenix VAL-MS 230 ST is listed as a Type 2 plug. The 230 in that type code is the maker’s 230 V family. The Uc is the figure on the device label, not a guess from the number in the name. A family title can also hide two types. The CHINT NU6-II / NXU-I+II listing covers 2-pole and 4-pole AC arresters, and the name includes both a Type 2 style code (II) and a Type 1+2 style code (I+II). The linked variant is the 4-pole, 40 kA unit. Read the front of the cartridge. Do not assume every unit in that family is the same type.

Uc, Up, In and Imax

Uc, the continuous voltage

Uc is the highest voltage that may sit on the SPD forever without it conducting. It has to be above the real system voltage, including the high side of a supply that swings. On a 230/400 V system, 275 V and 385 V ratings are both common. A 275 V device is the usual L-N choice where the phase voltage stays comfortably below that. Where a phase spends time up near or above 275 V, a 275 V SPD starts to conduct on ordinary mains and ages. A higher Uc, such as 320 V or 385 V, survives that swing and usually lets a little more residual voltage through. Measure the supply, or know how high it goes, before you pick. Do not copy the neighbour’s board.

The catalogue has both. A CNC YCS6-B is listed as 2-pole, 275 V, Imax 40 kA. The replacement cartridges are listed separately as 275 V, In 20 kA and 385 V, In 20 kA. A Suntree 2-pole unit is listed as 275 V, 40 kA. A Schneider iPR40 is listed as 4-pole, 440 V, 40 kA. On a three-phase device, 440 V may be the voltage between lines rather than the phase-to-neutral Uc. The label settles it. Match the cartridge to the base. A 385 V cartridge in a position the scheme designed for 275 V, or the other way round, is a different protective level.

Up, the voltage the equipment still sees

Up is the voltage protection level: the residual voltage across the SPD while it is discharging a standard test current. The equipment downstream has to withstand that. Sensitive electronics want a low Up. A low Up is not free. The device that achieves it may need a specific upstream SPD, and a long connecting lead adds its own voltage on top of Up, which is why the leads have to be short. If the catalogue title does not state Up, it is on the label and the datasheet. Do not invent it from the kA figure. A higher discharge current does not mean a lower Up.

In and Imax

For a Type 2 device, In is the nominal discharge current, an 8/20 microsecond wave it must survive repeatedly, and the current at which Up is measured. Imax is a higher 8/20 current it is tested to withstand a limited number of times. Imax is not the current it can pass every storm for twenty years. The CNC pair above is the distinction in one family: one listing is Imax 40 kA, the cartridge listings are In 20 kA. Compare In with In, or read both. A TOMZN TZG-40B and the CHINT 4-pole unit are listed with 40 kA in the family name or the variant, and the title does not say whether that 40 kA is In or Imax. Look at the symbol on the front before you treat it as the repeated rating.

Type 1 uses Iimp, the 10/350 impulse current, not Imax. A Type 1+2 device states both. A bigger number is more withstand, and it is only useful if the type is the one that location needs. A 40 kA Type 3 does not take the place of a Type 1 at a service entrance. There is no national kA to memorise. Exposed overhead lines and sites with a lightning protection system are where the higher Type 1 impulse rating earns its place. A board full of drives and PLCs still wants a Type 2 even when the service is quiet.

AC boards and DC solar arrays

AC SPDs for low-voltage power follow IEC 61643-11. PV SPDs follow IEC 61643-31. The tests are not interchangeable. DC does not pass through zero, and an array voltage on a cold morning is higher than the voltage at noon. The figure that must sit above that cold open-circuit voltage is Ucpv, not the Uc of a 275 V AC unit. How to find the cold string voltage is in the solar DC breaker guide. An SPD on the DC side has to be rated above that result.

Listings that say they are DC or PV parts include a Schneider G2040PV at 1,000 V DC, 2-pole, a CNC YCS6-C at 1,000 V DC, a TOMZN TZG40-PV at 1,200 V DC, and a CHINT Ex9UEP at 600 V DC, 40 kA. A 600 V DC unit does not belong on a string whose cold open-circuit voltage is above 600 V. A 1,200 V unit is not “better” on a small 2-panel string if the rest of the scheme was designed around a lower Ucpv and a stated Up. Match Ucpv to the array, with margin, and follow the inverter manual for the connection. Transformerless inverters are particular about whether the SPD is a Y or a U arrangement and about which pole is earthed. The manual is the drawing.

The TENSE TEN2-DC40 is listed as a 2-pole DC SPD, 40 kA, IP20. The title does not state the PV voltage. Read Ucpv on the label before it goes on an array. The Suntree 275 V unit is an AC listing. It does not go on the DC string. Fit DC protection on the array side and AC protection on the inverter output. They are two devices.

Where to install them

Think in layers. Type 1, if the entrance needs it, at the main incoming device. Type 2 on the main distribution board, and another Type 2 on a sub-board that feeds a workshop full of drives if that board is far from the first. Type 3 at the PLC, the VFD or the instrument rack when the upstream Up and the cable length say the equipment is not yet protected. One SPD at the meter, with twenty metres of cable and then a drive, is not the whole job.

The poles follow the system. A single-phase board is often 1-pole plus N, or 2-pole. A three-phase board is often 3-pole plus N. Whether the neutral is protected, and how the SPD connects to earth, depends on the earthing system (TN-S, TN-C-S, TT or IT). That is an electrician’s choice from the supply, not a guess from a 4-pole picture. A 4-pole device on a supply that must not have the neutral referenced that way is the wrong device even when the kA looks right.

Leads are part of the rating. A long live lead and a long earth lead add voltage while the current is changing, so the equipment sees more than Up. The usual installation rule is to keep the total connecting length to about half a metre, with no loops, and to take the earth to the board’s earth bar by the shortest route. A neat loop of spare wire around the trunking is a worse protector. Some boards use a V-connection, supply in one side and load out the other, so the SPD is not on a stub. Use the drawing that came with the device.

The SPD needs the back-up fuse or breaker the maker prints, not a breaker chosen because it was in the bin. Too small, and it opens on a surge and leaves you unprotected. Too large, and it may not protect the SPD against a short. The MCB, MCCB and RCCB guide explains the device types. The amp rating and the breaking capacity are the ones in the SPD instructions. Surge current flowing to earth can also trip an RCCB. The usual cure is the maker’s arrangement, often with the SPD on the supply side of the residual-current device, not an RCCB turned up or removed.

Look at the indicator after storms and during maintenance. A window that has changed colour, or a remote contact that has dropped out, means the cartridge is spent. The CNC listings include cartridges for that reason. Replace like for like: same type, same Uc, same poles. Do not leave a base with an empty or welded module and call the board protected.

A small factory board, worked through

A three-phase shop in Lahore has a 230/400 V main board, no lightning rod, and a VFD on a sub-board 15 m away. The main board gets a Type 2, 4-pole if the earthing system wants the neutral included, with Uc chosen from how high the phase voltage actually goes: a 275 V device if it stays well below that, a higher Uc if the supply is known to run hot. The kA on the order is read as In or Imax from the label, not from the advert line. The back-up breaker is the one the SPD sheet names, from the circuit breakers range. Leads are short, down to the earth bar. The sub-board, because of the distance, gets its own Type 2 or a Type 3 at the drive, coordinated with the first. If the roof later gains a PV array, the array gets a DC PV SPD whose Ucpv is above the cold string voltage, and the inverter output gets AC protection. The 275 V AC unit is not moved onto the string to save a device.

Selection checklist

1. Location: Type 1 at an exposed entrance, Type 2 at distribution boards, Type 3 at equipment that is still too far from the Type 2.
2. System: single-phase or three-phase, with or without neutral, and the earthing system.
3. Uc above the highest normal voltage. Ucpv above the cold array voltage on DC.
4. In, and Imax or Iimp, read as the symbols say. Up low enough for the equipment, with the maker’s coordination.
5. Back-up fuse or breaker exactly as the SPD sheet, and the SPD placed so it does not nuisance-trip the RCCB.
6. Leads short and straight, earth bond solid, indicator visible.
7. AC and DC devices kept on their own sides of an inverter.

Browse surge and lightning protection, circuit breakers for the back-up device, and solar accessories for array-side parts. Brands on the site include CHINT, Schneider Electric, Phoenix Contact, CNC Electric, Suntree, Tense and TOMZN. Prices are in PKR. Send a photo of the board, the supply voltage and any existing SPD label on WhatsApp and our Lahore team will help you match the type and Uc.