Advanced-protection BNCB5kA User Manual download pdf

(800) 237-4567 · (727) 535-6339 · Fax (727) 539-8955

www.aptsurge.com · inf[email protected]

Advanced Protection Technologies, Inc.

14550 58th Street North, Clearwater, Florida 33760

SPD SPD

SPD

BUILD ING

S ECOND AR Y S PD

PR IMAR Y S PD

COAX CABLE

Secondary SPD

(UL 497A) with better

clamping performance

to better protect

Primary SPD

(UL 497C) for life safety

purposes to protect

against Power line cross

or direct stroke

Protecting Coax Cables from Surges

Most surges on coax cable originate on the shield, not the pin.

• In a coax application, the pin is protected by the shield. For

example, lightning induces onto the shield, as would accidental

contact with a power line. Consequently, excessive emphasis on

protecting the pin may be misguided.

• According to IEEE C62.43 research:

– Surge current injected equally onto the pin and shield will

propagate unequally. Due to inductance, the shield will carry

about four times more surge current than the pin.

• “Surge propagation speed is faster on the shield than the pin,

leading to voltage differentials between pin and shield on long

runs of coax cable.”

• Coax surge protection is different than AC power surge protection:

– Focus is on the grounded shield conductor as opposed to the

‘active’ conductor. (On AC systems, focus is usually on the

energized conductor.)

– MOV suppression components may degrade signal quality due to

higher capacitance.

Primary & Secondary SPDs are intended for use together in a

cascade arrangement.

• Irony: People routinely protect AC circuits with sizeable cascade

SPDs, but do not do it with coax, despite smaller SPDs and

sometimes a harsher environment. Cascade SPDs as appropriate.

UL 497 Listing categories are often misunderstood.

• UL has two generalized categories for Communication SPDs:

Primary and Secondary Protectors.

– Primary Protectors: e.g., UL 497, UL 497C. “Primary protectors

are intended to suppress abnormal overvoltage conditions that

may exist on the circuit due to accidental contact with electric

light or power conductors operating at or over 300 V to ground…”.

Translation: These are more intended for life safety protection

from power line crosses & lightning, and may not clamp low

enough to protect sensitive electronics.

– Secondary Protectors: e.g., UL 497A. “Secondary protectors are

intended to suppress abnormal voltage and/or current conditions

that bypass the primary protector.”

Translation: Secondary Protectors offer better clamping

protection for sensitive electronics.

• Hiccup?: There are single SPDs having the robust componentry

of Primary SPDs and the lower and better clamping performance

of Secondary SPDs. However, by quirk, the lower clamping

voltage and better performance prevents them from passing

UL’s testing as a Primary Protector. The resulting confusion

factor is one reason why various manufacturers do not UL List

coax SPDs. Note that UL 96A Lightning Protection applications

mandate a UL 497C unit. Good practice suggests an additional

Secondary Protector to protect sensitive electronics.

Hiccup: Ground Loops and resulting signal loss

• Coax cable shields are grounded at their ‘head-end’. The shield is

not supposed to be grounded further downstream. Reason: If the

shield is grounded at multiple locations, and those grounds are at

different potentials, then current will ‘loop’ through the shield as the

ground potentials attempt to equalize themselves. This is called a

Ground Loop, and can/will cause signal decay.

• Away from the ‘head-end’, if the SPD’s shield protection is directly

connected to ground, it can/will cause a ground loop. Different SPD

technology with ground isolation is required to prevent this. The APT

SPD will not cause ground loops.

Concept of Cascade Protection

Avoiding Ground Loops

SPD

If these two grounds have a voltage difference, and

the coax Shield can complete the circuit, then current

will flow through the Shield creating a Ground Loop.

COMMUNICATION

EQUIPMENT

Head-End Coax

Shield is Referenced

to Ground

If remote SPD shield is ‘hard-grounded’ and there

is a voltage between the two grounds, then a

Ground Loop is likely. An SPD with ground

isolating qualities is required (APT BNCA10kA).

COAX CABLE

05.29.14.jb

Summary of Contents

Page 1 - Avoiding Ground Loops

(800) 237-4567 · (727) 535-6339 · Fax (727) 539-8955www.aptsurge.com · [email protected] Advanced Protection Technologies, Inc.14550 58th Street North

Related models: BNCA10kA

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Advanced-protection BNCB5kA User Manual

Browse online or download User Manual for Accessories for electrical Advanced-protection BNCB5kA. Advanced Protection BNCB5kA User Manual

Summary of Contents

Related models: BNCA10kA

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