Low voltage classification

JLoera

Member
In reference to Satellite Installations, what max voltage is considered for low voltage classification and if that is for operating voltage or just exposed cable voltage. Where would this be found in the NEC book to reference too?
 

paulengr

Senior Member
In reference to Satellite Installations, what max voltage is considered for low voltage classification and if that is for operating voltage or just exposed cable voltage. Where would this be found in the NEC book to reference too?
All low voltage telecom type circuits are chapter 7.

Read the introduction in NEC carefully. Chapters 1-3 apply generally. Chapter 4 is special equipment and 5 and 6 are special locations. These 3 chapters apply modifications to chapters 1-3.

Unlike those chapter 7 ignores chapter 1-3 unless it specifically calls for it. For instance in the past simply laying coax or CAT5 across a drop ceiling was acceptable (no reference to chapters 1-3). In recent years now it must now be in a raceway, same as general wiring.

It’s not so much a voltage consideration (even up 120 V is allowed in some cases) but it’s a matter of being power limited that sets chapter 7 apart. Generally up to 48 VDC with a few watts is a common telecom voltage. You can run 120 V circuits in the same raceway under limited circumstances for instance.

Satellite LNAs and LNBs today use generally proprietary systems where they inject 12-48 VDC onto the RG-6 to carry power to the LNB. The old K band stuff used an inline power supply but most receivers have it built in and just use a brand specific LNB these days. Some of it originally ran 120 V out to the dish. This is also used for steering motors with K/Ka band or say polar or geosynchronous orbits. The actual RF signals are under 1 V. The low noise amplifier just mildly amplifies and filters the signal to avoid noise from the cabling.
 

tom baker

First Chief Moderator
Staff member
All low voltage telecom type circuits are chapter 7.

Read the introduction in NEC carefully. Chapters 1-3 apply generally. Chapter 4 is special equipment and 5 and 6 are special locations. These 3 chapters apply modifications to chapters 1-3.

Unlike those chapter 7 ignores chapter 1-3 unless it specifically calls for it. For instance in the past simply laying coax or CAT5 across a drop ceiling was acceptable (no reference to chapters 1-3). In recent years now it must now be in a raceway, same as general wiring.

It’s not so much a voltage consideration (even up 120 V is allowed in some cases) but it’s a matter of being power limited that sets chapter 7 apart. Generally up to 48 VDC with a few watts is a common telecom voltage. You can run 120 V circuits in the same raceway under limited circumstances for instance.

Satellite LNAs and LNBs today use generally proprietary systems where they inject 12-48 VDC onto the RG-6 to carry power to the LNB. The old K band stuff used an inline power supply but most receivers have it built in and just use a brand specific LNB these days. Some of it originally ran 120 V out to the dish. This is also used for steering motors with K/Ka band or say polar or geosynchronous orbits. The actual RF signals are under 1 V. The low noise amplifier just mildly amplifies and filters the signal to avoid noise from the cabling.
*Most low voltage telecom circuits are in chapter 8, Communications Systems. coax is in Art 820. Grounding for sat dishes is in Art 810
*Section 90-3 Code Arrangement tells us Chapters 1,2,3, and 4 (not 1-3) apply generally. Whats important is Chapter 8 is not subject to the provisions of Chapters 1-7 unless those requirements are in Chapter 8. For example there is no burial depth for telephone lines
*There is no requirement for coax or or Cat 5 to be in a raceway, if there is please post that code section
*120 volts is not allowed in the same raceway with telecom, please post code section that allows that
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
In reference to Satellite Installations, what max voltage is considered for low voltage classification and if that is for operating voltage or just exposed cable voltage. Where would this be found in the NEC book to reference too?
Probably better to ask first why are you asking this.

One would assume that you are just a sat installer and in that case your reference would be Art 810 and 820. You wouldn't need to concern yourself with voltages since the manufacturers have that covered. That's why there is no mention of it.

However, if you are designing equipment or an unusual or commercial installation that's another story. Let us know.

-Hal
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
All low voltage telecom type circuits are chapter 7.
Satellite systems are covered by Article 810. Chapter 8 articles are "stand alone" and nothing in Chapters 1-7 applies unless specifically cited in the Chapter 8 Article.

Read the introduction in NEC carefully. Chapters 1-3 apply generally. Chapter 4 is special equipment and 5 and 6 are special locations. These 3 chapters apply modifications to chapters 1-3.
That is not what 90.3 says.

Unlike those chapter 7 ignores chapter 1-3 unless it specifically calls for it. For instance in the past simply laying coax or CAT5 across a drop ceiling was acceptable (no reference to chapters 1-3). In recent years now it must now be in a raceway, same as general wiring.
For Chapter 7 Articles the rules in Chapters 1-4 apply unless the chapter 7 article says that they don't.
 

JLoera

Member
Probably better to ask first why are you asking this.

One would assume that you are just a sat installer and in that case your reference would be Art 810 and 820. You wouldn't need to concern yourself with voltages since the manufacturers have that covered. That's why there is no mention of it.

However, if you are designing equipment or an unusual or commercial installation that's another story. Let us know.

-Hal
We are working on a new design and want to make sure that we meet all low voltage requirements.
 

tom baker

First Chief Moderator
Staff member
In that case you should be talking to UL or anther similar listing and testing agency. The NEC is an installation standard, not for designs. In many areas if the "whatever" you are designing is not listed, it can't be used. Washington has required product listing since 1935
 
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