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| What is the smallest bend radius and what is its purpose? |
| The smallest bend radius is 6 inches, and it is to prevent arcing under high voltage conditions, such as GPR caused by lightning or by a fault. Under these conditions, when there is a high voltage or high current on the CO cable, sharp edges or turns can cause puncturing of the cable jacket or arcing to equipment at local potential. |
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| How can the sealing current of the CO side be measured? |
There are two types of sealing currents that can be found on the line: simplex sealing current and loop sealing current.
Simplex sealing current: This type of current is found only on 4-wire circuits. A current source is applied between the transmit pair and the receive pair. To measure it, a current meter must be inserted in series with the Tip of the TX pair, and at the same time, a second meter must be inserted in series with the Ring of the TX pair. The total current flowing on the line is the sum of the readings on the two ammeters.
Loop sealing current: This type of current is found mostly on 2-wire circuits, but can also be used on 4-wire circuits. A current source is applied between the Tip and the Ring of the line. On 4-wire circuits, two different sources are used, one on the TX pair and one on the RX pair. To measure the current, an ammeter must simply be added in series with the Ring of the pair. This reading indicates the current flowing on the line.
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| How many spare cards are required for an installation? |
This depends on the type of circuits being isolated, on the required Mean Time Between Repair and on the size of the installation. It is usually recommended to have a spare of each model of card present on site, but if the installation size and the amount of cards are important, two cards might be a better option.
If it is a class A circuit, it is better to have at least one card of each model since service has to be reinstated fast upon the unlikely event of a failure.
If there are phone lines that are not critical to the plant, then a card can always be obtained on fast delivery, if necessary.
It is always possible to keep a 7501-16 card as a spare, since it can be used on DC circuits as well as POTS, modem, fax, DID lines and many more. Please see this product's installation guide for more information. |
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| What is the minimum safe distance required between shelves? |
| Due to the dielectric constant of the material used in the shelves and the thickness of the walls, the shelves can isolate up to 90 kV and therefore there can be no arcing between two shelves. But if the station side cables of one shelf are too close to the CO side cables of another shelf, an arc can occur during a GPR. For this reason, it is important to maintain a safe minimum distance of 1 foot (absolute minimum is 6 inches) between anything remote from equipment or wiring that are at local potential. |
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| Can a shelf be powered from a +24 Vdc? |
No. A shelf can only be powered from -24 Vdc referenced to the ground. If the only available power source is +24 Vdc, a 751324 power supply can be purchased from Positron; it will convert +24 Vdc to -24 Vdc, and will replace the 2 A fuse located on the side of the shelf which is provided with the 751324 power supply card (new fuse is 5 amp).
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| How should J14 be set in the 8-card shelf? |
The 8-card shelf should always be grounded using the ground lug on the right side of the shelf and J14 be left open. The only time J14 will be connected is when there is no ground available to ground the shelf and when an AC source is used with the 751313 power supply. In this specific case, the shelf can be grounded using the ground from the AC cable.
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| Which is preferable, using an external power supply or an internal plug-in power supply? |
Each power supply configuration has its advantages and disadvantages.
The internal power supply uses the shelf space very efficiently. With the internal power supply, it is possible to get a battery backup as a secondary unit or a second power supply for redundancy. The power supply is well protected against surges and disturbances. In the event of power supply failure, only that shelf is lost. If the circuit cards in the shelf do not consume all the power available from the power supply, it is possible to power external equipment from the -24 V provided by the plug-in power supply, up to a maximum of 0.75 A.
When using an external power supply, one unit can power multiple shelves. With this configuration it is important to make sure there is a battery backup, since in the unlikely event of a failure, more circuits would be lost. The heat dissipation of the power supply does not contribute to the temperature increase in the shelf, which can be a problem with the card operating to a maximum of 50°C.
** When using a plug-in power supply, if temperature is a problem because of the type of circuit card used, one can use a 751109/13F 8-card shelf with fan. This is a regular 751109/13 with the addition of a fan on the left side of the shelf that keeps the temperature of the shelf just a couple of degrees above ambient.
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| What is the wire size and dielectric strength of the CO side of the Positron provided cable? |
| The previous cable used was 22 gauge and was rated at 20,000 V. However, this cable is no longer being manufactured. The current cable in use has a conductor size of 22 gauge. The core to shield dielectric rating by the manufacturer is 10,000 V. Positron has tested the cable to 20,000 V with no breakdown. At this time Positron has been unsuccessful at finding an Air Core cable rated at 20,000 V and with definitive physical characteristics. |
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| Why not use a standard 66 block instead of the ADC HV jacks on the red side of the board? |
There are many reasons:
1. The dielectric strength on an empty 66 block is 350 V. A block with cable pairs punched down is less than 280 V.
2. The breakdown on most electric type connecting blocks is 600 V or less.
3. The breakdown on the cable pair is a minimum of 5000 V pair to pair, some are as high as 10,000 V pair to pair, well above a 66 block capacity.
4. The use of a 66 block is not approved by I.E.E.E. standard 487 1980, 1992, or the current 2000 version, along with Telcordia Practice 876-310-100, due to their dielectric rating.
5. The ADC isolation jacks (20,000 V Rating) offer testing and maintenance functions in addition to a connectivity function. If a person is careful, cross connecting (revising where a pair is tied down) can be accomplished if necessary on the CO side of the Jacks, but it is indeed cautioned.
6. The dielectric rating of all of the equipment including the PC board is well above a 66 block or other normal telephone punch blocks.
7. The 66 blocks have been seen being destroyed by arcing on the CO side, but the cable pairs, shelf connections, and PC board components were not at all effected by the event.
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| Which cards will work with the old shelves? |
The various versions of the Teleline shelves are listed below, with the associated compatible cards:
7501-08: This is the oldest version of the 8-card shelf; it is made of fiberglass panels glued together with epoxy. The compatible cards are:
•Any 2-wire card (751311, 751317, 7501-72, 7501-06A, 7501-05, 751340, 7501-15A/B/C, 7501-16A/B/C, 751333A and 751321 (without the expandable piggyback)
•The line test card 751366 (the alphanumerical pair will not be used)
The non-compatible cards are:
•Any 4-wire card (7501-24, 751339, 751329, 751321C and 751321B)
•Any small plug-in power supply (751313, 751316, 751324 and 751312 battery back-up)
The shelf is not compatible with the four wires DX signaling line setup using the holding coil 7501-40.
751101: This is the first version of the molded 8-card shelf. The following is compatible with this shelf:
•Any card
•The 4-wire DX signaling line setup
The small plug-in power supplies are not compatible with this shelf.
751109: This is the newest 8-card shelf; every Teleline card, power supply and setup is compatible with this shelf.
7501-27: This is the old version of the 3-card shelf; it is made of fiberglass panels glued together with epoxy. The compatible cards are:
•Any 2-wire card (751311, 751317, 7501-72, 7501-06A, 7501-05, 751340, 7501-15A/B/C, 7501-16A/B/C, 751333A and 751321 (without the expandable piggyback)
•The line test card 751366 (the alphanumerical pair will not be used)
The non-compatible cards are:
•Any 4-wire card (7501-24, 751339, 751329, 751321C and 751321B)
•Any small plug-in power supply (751313, 751316, 751324 and 751312 battery back-up)
The shelf is not compatible with the four wires DX signaling line setup using the holding coil 7501-40.
7501-09: This is the old version of the 5-card shelf; it is made of fiberglass panels glued together with epoxy. The compatible cards are:
•Any 2-wire card (751311, 751317, 7501-72, 7501-06A, 751340, 7501-15A/B/C, 7501-16A/B/C, 751333A and 751321 (without the expandable piggyback)
•The line test card 751366 (the alphanumerical pair will not be used)
The non-compatible cards are:
•Any 4-wire card (7501-24, 751339, 751329, 751321C and 751321B)
•Any small plug-in power supply (751313, 751316, 751324 and 751312 battery back-up)
The shelf is not compatible with the four wires DX signaling line setup using the holding coil 7501-40.
751112: This is the newest 5-card shelf; every Teleline card, power supply and setup is compatible with this shelf.
751127: This is the most recent version of the 3-card shelf. Any Teleline card and setup is compatible with this shelf. Plug-in power supplies are not compatible with this shelf. The cards have to be powered from an external power supply module.
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| When installing an HDSL circuit, can the station equipment be powered from the CO? |
The HDSL card cannot pass the DC current to the station side. The station equipment should be powered locally. If the equipment must be powered through the Teleline card, a 4-wire DX signaling setup must be installed. To do so, the following is required:
•Two 751340 2-wire HDSL cards
•One 7501-16 OPX card to feed the DC
•One 7501-40 holding coil to reinsert the DC
Or:
•One 751339R3
•Two 751340R3
For more information on how to install this setup, refer to the installation guide on the holding coil 7501-40. |
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