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Paperless Datasheet
Going green and protecting environment is manufacturers' responsibility. Each WatchfulEyE product has a link of downloading data sheet on its enclosure:

3D file download

Model & Ordering Code

Model Ordering Code MCOV/Uc Remote Contacts UPC/EAN Code
WTH-120/B/R/1P-275 US120304 275VAC YES (0) 811914030904
WTH-120/B/1P-275 US120294 NO (0) 811914030959
WTH-120/B/R/1P-320 US120305 320VAC YES (0) 811914030911
WTH-120/B/1P-320 US120295 NO (0) 811914030966
WTH-120/B/R/1P-385 US120306 385VAC YES (0) 811914030928
WTH-120/B/1P-385 US120296 NO (0) 811914030973
WTH-120/B/R/1P-420 US120307 420VAC YES (0) 811914030935
WTH-120/B/1P-420 US120297 NO (0) 811914030980

Certificates of Products

Note: MCOV 385VAC UL listed only

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More Package
Model with suffix WTH-120/B/R/1P-275 x2pcs x3pcs x4pcs
Ordering Code US120304 US120304x2 US120304x3 US120304x4
Model with suffix WTH-120/B/1P-275 x2pcs x3pcs x4pcs
Ordering Code US120294 US120294x2 US120294x3 US120294x4
Model with suffix WTH-120/B/R/1P-320 x2pcs x3pcs x4pcs
Ordering Code US120305 US120305x2 US120305x3 US120305x4
Model with suffix WTH-120/B/1P-320 x2pcs x3pcs x4pcs
Ordering Code US120295 US120295x2 US120295x3 US120295x4
Model with suffix WTH-120/B/R/1P-385 x2pcs x3pcs x4pcs
Ordering Code US120306 US120306x2 US120306x3 US120306x4
Model with suffix WTH-120/B/1P-385 x2pcs x3pcs x4pcs
Ordering Code US120296 US120296x2 US120296x3 US120296x4
Model with suffix WTH-120/B/R/1P-420 x2pcs x3pcs x4pcs
Ordering Code US120307 US120307x2 US120307x3 US120307x4
Model with suffix WTH-120/B/1P-420 x2pcs x3pcs x4pcs
Ordering Code US120297 US120297x2 US120297x3 US120297x4

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In accordance with: IEC/EN61643-11 - Class I and UL1449 Type 4 Location
Location of use: main sub-distribution boards
One-piece compact design with minimized volume but maximized capability of Class I surge protection.
Internal thermal disconnect devices help ensure safe or at end-of-life
WTH-120/B/R/1P Series Technical Data
Requirement Class to IEC/EN61643-11 Class I
IEEE Category Rating C & B
Nominal Discharge Current (In) 60kA
Max. Discharge Current (Imax) 120kA
Pulsed Current (Iimp) 15kA
Protection Modes L-PE, N-PE
Protective Element MOV
Follow Current (If) NO
Response Time (tA) <5ns
Leakage Current (at 75%U1mA) <20μA
Thermal Protection YES
Protection Rating (IP Code) IP 20
Short Circuit Current Ratings (SCCR) 25kA rms
Max. Back-up Fuse (if mains >160A) 160A gL (circuit-breaker: <100A)
Surge Life at 3kA (8/20μs) >5000 events
Temperature Range - 40°F to 176°F (-40°C to 80°C)
Relative Humidity 0% to 95% noncondensing
Maximum Operating Altitude 10,000 feet (3000m)
Terminal Cross Section 35mm² (solid) / 25mm² (stranded)
Stripping Length Contacts 0.6inches (15mm)
Terminal Screw Torque Max. 3.5Nm
DIN Rail EN60715 35mm top-hat rail
Dimensions DIN 43880 36mm (2TE)
Housing Material Thermoplastic (UL94 V-0)
Housing Design One-piece compact design
Net Weight Per Unit 0.46Lb (209g)

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Surge Protection Connection Diagram

Indication of three levels of surge protection
With three MOVs' protection at the same time, the module can realize Class I surge protection; in case that two of the indicator windows indicates red, it can still meet Class II surge protection requirements.

Maximum Continuous Operating Voltage (MCOV/Uc) 275VAC 320VAC 385VAC 420VAC
Voltage Protection Level (Up) 2.1kV 2.2kV 2.4kV 2.5kV
Residual Voltage (Ures) 1.0kV 1.1kV 1.2kV 1.4kV


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Remote Contacts (Dry Contacts)
1: COM (Common)
2: NC (Normally Close)
3: NO (Normally Open)

Contact Ratings 125VAC/3A, 250VAC/1.5A
Terminal Cross Section Max. 1.5mm²
Stripping Length Contacts 0.25 inches (6-7mm)
Remote Terminal Torque 0.25Nm

Fault Indication

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Common Terms and Definitions
1. Normal operating voltage rating (Un)
2. Maximum Continuous Operating Voltage (Uc/MCOV):
Maximum r.m.s. voltage, which may be continuously applied to the surge protective device's mode of protection.
3. Nominal Discharge Current for Class II Test (In):
crest value of the current through the surge protective device having a current waveshape of 8/20μs.
4. Maximum Discharge Current (Imax):
Crest value of a current through the surge protective device having an 8/20μs waveshape and magnitude according to the manufacturers specification. Imax is equal to or greater than In.
5. Voltage Protection Level (Up):
Maximum voltage to be expected at the surge protective device terminals due to an impulse stress with defined voltage steepness and an impulse stress with a discharge current with given amplitude and waveshape.
6. Residual Voltage (Ures):
Crest value of voltage that appears between the terminals of an surge protective device due to the passage of discharge current.
7. IEEE 62.41
CATEGORY C: outdoor overhead lines, service entrance (most severe)
CATEGORY B: major feeder, short branch circuits, service panel (indoor)
CATEGORY A: long branch circuits, receptacles (indoor) (least severe)

How to choose a suitable Uc(MCOV) value
Note: Uc >1.15Un
The relationship between two parameters Uc and Up of a surge protective device is proportional.
If Uc is small, the value of Up is also small; surge protective devices with smaller Up can provide better surge protection.
Whether to choose smaller Uc depends on the voltage stability of the grid.
If you choose surge protective devices with smaller Uc for the grid with instable voltage, the surge protective devices will frequently work while the grid voltage fluctuates, resulting in shortening surge protective device's product life.
If you choose larger Uc, and the value of Up is accordingly large, the surge protective efficiency will not be so fine.
If you are unsure of the voltage stability of the grid,
it is suggested to calculate MCOV(Uc) using the following formula: √ 2  Un < Uc < √ 3 Un

AC Network (Un) MCOV(Uc), L/N-PE Protection Mode
110V, 120/208V, 127/220V 150V
220/380V 275V, 320V, 385V
230/400V 275V, 320V, 385V, 420V
240/415V 320V, 385V, 420V
266/460V, 277/480V 385V, 420V
347/600V 550V, 690V
Wind Power System 690V (Grid side ), 885V (Gen side )

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AC Network Connection Diagram (1/2)

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AC Network Connection Diagram (2/2)

Difference mode & Common mode Connection Diagram

Common mode:L-PE, N-PE surge protection
Difference mode:L-N surge protection

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Selection of back-up fuse

Selection of back-up circuit-breaker

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1. Origin of the installation
2. Distribution board
3. Distribution outlet
4. Main earthing terminal or bar
5. Surge protective device, class I or II tested
6. Earthing connection (earthing conductor) of the surge protective device
7. Fixed equipment to be protected
8. Surge protective device, class II tested
9. Surge protective device, class II or class III tested
10. Decoupling element or line length
F1, F2, F3 overcurrent protective disconnectors
NOTE Refer to IEC 61643-12 for further information.

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N-PE Module
WTH-165/G module integrates High-Energy GDT, no leakage current. It pairs WTH-120/B/R series surge protector, combined into N-PE protection mode, the two modules are the same in dimension and shape, and are connected with a dedicated bus-bar to achieve a perfect combination.
WTH-165/G Technical Data
Max. continuous operating voltage (Uc) 255V
Nominal Discharge Current (In) 80kA
Max. Discharge Current (Imax) 165kA
Pulsed Current (Iimp) 52.5kA
Voltage protection level (Up) 1.5kV
Protection Modes N-PE only
Protective Element High Energy GDT
Follow Current (If) 100A rms
Response Time (tA) <100ns
Net Weight Per Unit 0.4Lb (180g)

3P + NPE Combintion Package
Model with suffix Ordering Code Model with suffix Ordering Code
WTH-120/B/R/1P-275 x3pcs +NPE US120304x3N WTH-120/B/1P-275 x3pcs +NPE US120294x3N
WTH-120/B/R/1P-320 x3pcs +NPE US120305x3N WTH-120/B/1P-320 x3pcs +NPE US120295x3N
WTH-120/B/R/1P-385 x3pcs +NPE US120306x3N WTH-120/B/1P-385 x3pcs +NPE US120296x3N
WTH-120/B/R/1P-420 x3pcs +NPE US120307x3N WTH-120/B/1P-420 x3pcs +NPE US120297x3N

1P + NPE Combintion Package
Model with suffix Ordering Code Model with suffix Ordering Code
WTH-120/B/R/1P-275 +NPE US120304x1N WTH-120/B/1P-275 +NPE US120294x1N
WTH-120/B/R/1P-320 +NPE US120305x1N WTH-120/B/1P-320 +NPE US120295x1N
WTH-120/B/R/1P-385 +NPE US120306x1N WTH-120/B/1P-385 +NPE US120296x1N
WTH-120/B/R/1P-420 +NPE US120307x1N WTH-120/B/1P-420 +NPE US120297x1N

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FAQ & Help
1. What should I do if I can't find the paper manual in the product packaging?
Watchful Eye products is committed to going green with paperless data sheets. On the side of each product enclosure is an engraved link with URL for downloading paperless data sheet and QR code of the website. If you need the paper data sheet, you can open the link and print the data sheet by yourself.

2. The advantages of fault indication windows?
If surge protection fails, the fault indication windows will turn red, thus it can be seen intuitively, and the surge protective device can be replaced in time to avoid damage to the equipment caused by a second surge.

3. What instruments can be used to test whether its surge protection function is normal or not?
Test with a Watchful Eye surge protector tester

4. Can you list more applications?
Power supply panel, whole house

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Download WatchfulEyE Official App
To learn about more products and updates from company, please scan QR code to download the official App:

After-sale Services
Watchful Eye provides a 5-year quality warranty globally.

I have a question

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